Creatinine Clearance Calculator – Cockcroft-Gault CrCl with the 2021 CKD-EPI eGFR
One blood test, two standard estimates of how well your kidneys filter.
Your details and lab result
🔒 Everything is calculated in your browser — your numbers never leave your device.
Your kidney function estimates
| Estimate | Value | Range |
|---|---|---|
| Cockcroft-Gault CrCl (dosing) | 74.1 mL/min | 60–89 · Mildly decreased |
| CKD-EPI 2021 eGFR (lab reports) | 69.2 mL/min/1.73 m² | 60–89 · Mildly decreased |
🩺 Both numbers are estimates built from one blood result — neither measures your kidneys directly. Muscle mass, a meat-heavy meal, creatine supplements and some medicines can all move creatinine without your kidneys changing at all. A single estimate is a starting point for a conversation with your clinician, never a diagnosis.
Advanced options — weight basis and live comparison
These extra controls use the same live calculation as the calculator above — open Advanced options to set your height and weight basis, and to see all three weight-basis clearances compared live against eGFR.
Live weight-basis comparison
Add your height above to see ideal and adjusted weight for your own numbers.
Ideal body weight (Devine): — · Adjusted body weight: —
| Weight basis | Weight | CrCl |
|---|
eGFR for comparison (CKD-EPI 2021): — · Gap between the headline clearance and eGFR: —
This panel recomputes independently from your inputs and never changes the headline result. It shows the arithmetic spread only; which basis applies to any real decision is a question for your prescriber or pharmacist.
One blood test, two standard estimates of how well your kidneys filter. This calculator works out your creatinine clearance with the Cockcroft-Gault formula — the one most drug labels still use for dosing — and puts the 2021 CKD-EPI eGFR from your lab report right beside it, with ideal and adjusted body-weight options when weight matters.
Key takeaways
- Creatinine clearance (Cockcroft-Gault, in mL/min) is the figure most medicine labels still use; eGFR (CKD-EPI 2021, per 1.73 m²) is the figure laboratories print and staging uses. They come from the same blood test and answer different questions.
- The weight fed into Cockcroft-Gault can move the answer across a whole range at high body weights: the worked example spreads from 101.9 mL/min on actual weight to 67.6 mL/min on ideal weight, with adjusted weight at 81.3 mL/min.
- Both numbers are estimates from one steady creatinine value, not measurements and not a diagnosis. A low or straddling result calls for a repeat test and a clinician conversation, never a dose change made from this page.
Contents
- Where your numbers sit
- Numbers that travel with kidney function
- From one blood result to two estimates
- The math behind the default example
- Two things worth knowing about these estimates
- CrCl versus eGFR: the same blood test, two different jobs
- Devine ideal weight and adjusted weight, worked step by step
- Cockcroft-Gault: where it came from, and where it strains
- How to read the two numbers together
- Creatinine clearance questions, answered
Where your numbers sit
The standard ranges clinicians group kidney function into (often labelled G1 to G5 for eGFR). Both of your markers are plotted — purple for Cockcroft-Gault clearance, teal for CKD-EPI eGFR. The ranges describe population groupings, not a diagnosis: what matters is a confirmed result over time, not one estimate.
Both estimates land in the 60–89 range for the default example — mildly below the 90-plus band, which is common by age 60 even with a “normal” creatinine.
| Range | Often labelled | Usually described as |
|---|---|---|
| 90 or above | G1 | Normal / high range |
| 60–89 | G2 | Mildly decreased range |
| 45–59 | G3a | Mild-to-moderate decreased range |
| 30–44 | G3b | Moderate-to-severe decreased range |
| 15–29 | G4 | Severely decreased range |
| under 15 | G5 | Kidney failure range |
Cockcroft-Gault (1976) — the headline
Built from 249 hospital patients, it estimates creatinine clearance in mL/min from age, weight, sex and one creatinine value. Nearly fifty years on, it is still the formula most medicine labels and pharmacy systems use to adjust doses for kidney function — which is why it leads this page.
CrCl = (140 − age) × weight ÷ (72 × creatinine), × 0.85 if female
It uses your real body size — a strength for dosing, and the reason weight choice matters.
CKD-EPI 2021 — the lab-report standard
The equation modern laboratories use to report eGFR automatically with every creatinine result. The 2021 version dropped the old race adjustment entirely. It expresses filtering per 1.73 m² of body surface — a standard size — so weight never enters it.
eGFR = 142 × (Scr/κ) terms × 0.9938^age, × 1.012 if female
Better for comparing people and tracking kidney health over time.
Numbers that travel with kidney function
Weight and muscle drive creatinine itself — these read the body-composition side of the same blood test.
From one blood result to two estimates
Three steps between the number on your lab report and the figures above.
Enter the creatinine
Serum creatinine from your blood test, in mg/dL or µmol/L, with your age, sex and weight. Creatinine is the waste product your muscles shed at a fairly steady rate — and your kidneys clear.
Cockcroft-Gault estimates clearance
The formula asks: at this age, with this much body producing creatinine at this blood level, how fast must the kidneys be clearing it? Weight stands in for muscle — imperfectly, which is why ideal and adjusted weights exist.
CKD-EPI checks it the lab’s way
The same creatinine runs through the 2021 CKD-EPI equation — no weight, normalised to a standard body size. Two honest methods rarely agree to the decimal; landing in the same range is the reassuring outcome.
The math behind the default example
Step 1 — the age factor. For a 60-year-old man: 140 − 60 = 80. The formula assumes filtering capacity and muscle mass fade with age, so every birthday shrinks the top line even if nothing else changes.
Step 2 — the top line. 80 × 80 kg = 6,400. Weight stands in for the muscle mass producing the creatinine.
Step 3 — the bottom line. 72 × 1.2 mg/dL = 86.4. The 72 is the formula’s unit constant; the creatinine is his actual blood level.
Step 4 — the clearance. 6,400 ÷ 86.4 = 74.1 mL/min. No 0.85 adjustment applies for a man. The CKD-EPI cross-check reads his creatinine against the typical male value (κ = 0.9): the ratio 1.2 ÷ 0.9 = 1.33 and the age term 0.9938⁶⁰ ≈ 0.688 pull its estimate to 69.2 mL/min/1.73 m² — same range, slightly lower number, exactly the pattern clinicians expect.
Two things worth knowing about these estimates
Why the formulas disagree — and why the weight you feed them matters so much.
They were built in different centuries, on different people, for different jobs. Cockcroft-Gault (1976) came from hospital patients and predicts the actual millilitres per minute a person’s kidneys clear — the figure a pharmacist needs to size a dose. CKD-EPI (2021) came from large research cohorts and predicts filtering relative to a standard body surface of 1.73 m² — the figure a lab needs to stage and track kidney health across a whole population.
So the gap between them is information, not error. On this page’s default example they read 74.1 and 69.2 — same range, a few points apart. They separate most where bodies differ most from “standard”: very heavy, very light, very muscular or very frail people. That is precisely where the weight options below the calculator earn their keep, and where a clinician’s judgement matters more than either formula.
Cockcroft-Gault treats every kilogram of you as creatinine-producing tissue. For a lean person that is roughly true. For someone carrying a lot of fat it is not — fat tissue sheds very little creatinine, so actual weight can flatter the estimate and suggest the kidneys are doing better than they are.
Clinicians answer this two ways, both offered here once you add your height. Ideal body weight (the Devine formula: 50 kg for a man, 45.5 kg for a woman, plus 2.3 kg per inch over five feet) estimates the lean frame alone. Adjusted body weight splits the difference — ideal plus 40% of the extra — and is a common dosing compromise. Neither is “the truth”; they are lenses. If the three answers land in different ranges, that spread is worth raising with whoever prescribes for you.
CrCl versus eGFR: the same blood test, two different jobs
Both numbers on this page come from the same creatinine result, yet they answer different questions. Confusing them is the single most common misunderstanding in kidney-function numbers, so it is worth stating the distinction plainly before anything else.
Creatinine clearance from Cockcroft-Gault is an absolute flow: millilitres of blood cleared of creatinine per minute, for this person, at this body size. That is why it takes weight as an input. Estimated glomerular filtration rate from CKD-EPI 2021 is a normalised rate: millilitres per minute per 1.73 square metres of body surface, the standard body size laboratories use so that results can be compared between people of different sizes. Weight never enters eGFR, because the normalisation has already removed body size from the picture. On the default example the two read 74.1 mL/min and 69.2 mL/min/1.73 m². They are close, they land in the same range, and they are still not the same quantity: one has a person attached to it, the other has a standard person attached to it.
| Feature | Creatinine clearance (Cockcroft-Gault) | eGFR (CKD-EPI 2021) |
|---|---|---|
| Unit | mL/min, absolute for this person | mL/min/1.73 m², normalised to a standard body size |
| Uses body weight? | Yes, weight stands in for muscle mass | No, weight never enters the equation |
| Typical home | Medicine labels and pharmacy systems | Laboratory reports and kidney-disease staging |
| Best question it answers | How fast is this body clearing creatinine? | Where does this person sit against population ranges? |
| Where it strains most | Very heavy, very light, very muscular or frail bodies | Very large or very small bodies, where normalisation hides absolute size |
The drug-dosing context is historical, and it is changing, and both halves of that sentence matter. Most medicine labels in force today were written from pharmacokinetic studies that used Cockcroft-Gault, so a label that quotes a clearance cut-off usually means a Cockcroft-Gault clearance in mL/min. That is why pharmacy systems still compute it, and why this page leads with it. At the same time, the United States Food and Drug Administration issued guidance in 2024 recommending eGFR-based assessment for pharmacokinetic studies in renal impairment, and a National Kidney Foundation consensus the same year supported moving medication-related decisions toward race-free eGFR equations. The honest summary is therefore a transition, not a switch that has already happened: labels largely still speak Cockcroft-Gault, newer guidance points toward eGFR, and a clinician or pharmacist checking a specific medicine needs to know which figure that medicine’s own label specifies. This page gives both figures precisely so that question can be answered from one set of inputs, and it gives no dosing recommendation of its own. Never start, stop or change a prescribed dose because of a number on this page.
There is one legitimate bridge between the two units, and it is worth knowing because it explains many apparent disagreements. To turn a normalised eGFR into an absolute flow for a particular person, multiply by that person’s body surface area and divide by 1.73. That is called de-indexing. As an illustration only, an eGFR of 69.2 mL/min/1.73 m² in a person whose body surface area is 1.9 m² becomes 69.2 × 1.9 ÷ 1.73 = 76.0 mL/min of absolute flow, which sits reassuringly close to the same example’s Cockcroft-Gault figure of 74.1 mL/min. The illustration is not a result for any real person, because body surface area itself has to be estimated from height and weight, but it shows why a large person can have an eGFR that looks modest while their absolute clearance is higher, and why a small person can show the reverse pattern. If you want the eGFR side explored on its own, with its own staging and ranges, see our GFR Calculator.
One more distinction belongs here because it is often missed. Neither figure measures the kidneys directly. True glomerular filtration is measured with an injected marker that is filtered and neither secreted nor reabsorbed, such as inulin or iohexol, which is impractical for routine care. Creatinine clearance overestimates true filtration somewhat because the kidney tubules secrete creatinine in addition to filtering it, so clearance counts secreted creatinine as if it had been filtered. eGFR is an estimate of filtration built from the same imperfect marker, fitted to large research populations. Both are therefore estimates with known biases, not measurements, and a gap between them is information about which bias is biting in this body, not proof that one of them is broken.
Devine ideal weight and adjusted weight, worked step by step
The calculator’s weight options look like a small detail. At high body weights they move the headline answer more than any other choice on the page, so they deserve a full worked example rather than a one-line definition.
Ideal body weight on this page uses the Devine formula, published in 1974 as a dosing rule of thumb. It starts from a base weight at five feet tall and adds a fixed amount for every inch above five feet: 50 kg for a man and 45.5 kg for a woman, plus 2.3 kg per inch over 60 inches. It is a height-only formula. It knows nothing about frame size, age or muscle, and it was never meant as a target weight or a healthy-weight judgement. It is a reference frame for dosing arithmetic, and it should be read that way. A muscular person can sit far above their Devine ideal weight while carrying very little fat, which is exactly why no single weight basis is right for every body.
Adjusted body weight splits the difference between the scale and the ideal frame. The formula used here, and the one most commonly quoted with the 0.4 factor, is: adjusted weight = ideal weight + 0.4 × (actual weight − ideal weight). The reasoning is that the extra weight above the ideal frame is not all fat and not all muscle either, so counting 40% of it approximates the creatinine-producing part. The 0.4 factor was validated in particular for aminoglycoside antibiotic dosing; it is a widely used convention rather than a universal constant, and different references use different factors or different thresholds. One practical rule from the literature is worth carrying: adjusted weight is meaningful only when actual weight exceeds ideal weight. If actual weight is below ideal weight, the usual practice is to use actual weight, not to let the adjusted formula drag the number below the ideal frame.
| Example | Height and weight | Ideal (Devine) | Adjusted (0.4 factor) | CrCl: actual / ideal / adjusted |
|---|---|---|---|---|
| A: man, 60, creatinine 1.2 mg/dL | 70 inches, 110 kg | 73.0 kg | 87.8 kg | 101.9 / 67.6 / 81.3 mL/min |
| B: woman, 55, creatinine 1.0 mg/dL | 64 inches, 95 kg | 54.7 kg | 70.8 kg | 95.3 / 54.9 / 71.1 mL/min |
Example A, step by step, using the engine’s own arithmetic. Ideal weight: 50 + 2.3 × (70 − 60) = 50 + 23.0 = 73.0 kg. Adjusted weight: 73.0 + 0.4 × (110 − 73.0) = 73.0 + 14.8 = 87.8 kg. Clearance on actual weight: (140 − 60) × 110 ÷ (72 × 1.2) = 8,000 ÷ 86.4 = 101.9 mL/min. On ideal weight the same numerator becomes 80 × 73.0 = 5,840, giving 67.6 mL/min. On adjusted weight it becomes 80 × 87.8 = 7,024, giving 81.3 mL/min. The spread from one person, one blood test, is 34.3 mL/min between the highest and lowest basis, and in this example it crosses a range boundary: the actual-weight figure sits in the 90-or-above range while the ideal and adjusted figures sit in the 60–89 range. That crossing is the whole point of showing all three. A prescriber who sees only the 101.9 figure and a prescriber who sees only the 67.6 figure would reason about the same patient differently, and the spread itself is the signal that the weight choice needs a clinical decision rather than a default.
Example B shows the same pattern with the female adjustment included. Ideal weight: 45.5 + 2.3 × (64 − 60) = 45.5 + 9.2 = 54.7 kg. Adjusted weight: 54.7 + 0.4 × (95 − 54.7) = 54.7 + 16.1 = 70.8 kg. Clearance on actual weight: (140 − 55) × 95 ÷ (72 × 1.0) = 8,075 ÷ 72 = 112.2, times 0.85 = 95.3 mL/min. On ideal weight: 85 × 54.7 ÷ 72 = 64.6, times 0.85 = 54.9 mL/min. On adjusted weight: 85 × 70.8 ÷ 72 = 83.6, times 0.85 = 71.1 mL/min. Here again the spread crosses a boundary, from 90-or-above on actual weight down to 45–59 on ideal weight, with adjusted weight landing in between at 60–89. The eGFR cross-checks, which ignore weight entirely, are 69.2 mL/min/1.73 m² for Example A and 66.5 mL/min/1.73 m² for Example B, both in the 60–89 range. Notice that the adjusted-weight clearances land closest to the eGFR range in both examples. That is suggestive, not proof: eGFR and adjusted-weight clearance are different quantities, and agreement between them does not settle which weight a particular medicine’s label requires.
| Weight basis | What it is | When references commonly use it |
|---|---|---|
| Actual weight | The number on the scale today | The classic default, and the usual choice when weight is near or below the ideal frame |
| Ideal weight (Devine) | Height-only reference frame | As the lower boundary of a clearance range, and for medicines that distribute poorly into fat |
| Adjusted weight (0.4) | Ideal plus 40% of the excess over ideal | As a common dosing compromise in obesity, where neither actual nor ideal alone fits |
Try the live comparison in the Advanced panel below the calculator: add your height, and the panel recomputes all three clearances from your own age, sex and creatinine, independently of the main result. If your three figures agree, the weight question is settled for practical purposes. If they spread across a boundary, bring the spread itself to your prescriber or pharmacist. The right response to a wide spread is never to pick the middle number and move on; it is to ask which basis the relevant reference specifies for the situation at hand.
Cockcroft-Gault: where it came from, and where it strains
A formula that has survived fifty years deserves both respect for what it does and honesty about the bodies it was never built for.
Cockcroft and Gault published their equation in 1976, derived from 249 hospital patients with measured creatinine clearance. The cohort was predominantly male and drawn from a single hospital population, which matters because every later limitation traces back to that starting point in one way or another. The equation is beautifully simple for bedside use: age, weight, sex and one creatinine value, with a single constant, 72, absorbing the unit conversions. Simplicity was the point. It was designed to replace 24-hour urine collections, which are cumbersome and error-prone, with a calculation any clinician could do by hand. It succeeded so completely that it became embedded in drug labelling, and that embedding is why it is still computed today even though more accurate population equations now exist for staging kidney disease.
The derivation also explains the formula’s most counterintuitive feature: the (140 − age) term. Age is not in the equation as a penalty for being old. It is there because the study population showed that clearance falls as people age, partly because kidneys filter less and partly because muscle mass, the source of creatinine, also falls. The term therefore does two jobs at once, and it does them crudely. The same creatinine value means very different things at different ages, which the page’s own arithmetic makes vivid. Take a man weighing 80 kg with a creatinine of 1.2 mg/dL. At age 30 his Cockcroft-Gault clearance is 101.9 mL/min and his CKD-EPI eGFR is 83.4 mL/min/1.73 m². At age 80, with the identical weight and creatinine, his clearance is 55.6 mL/min and his eGFR is 61.1 mL/min/1.73 m². Nothing about his blood test changed. His age did, and with it the interpretation. A creatinine that looks reassuringly normal on a lab slip can therefore hide substantially reduced function in an older adult, which is why guidelines insist on an age-adjusted estimate rather than the raw creatinine number.
| Situation | What goes wrong | What to keep in mind |
|---|---|---|
| Older age and frailty | Less muscle produces less creatinine, so the blood level flatters the kidneys | An apparently normal creatinine needs an age-adjusted estimate and a repeat test, not reassurance alone |
| Very high muscle mass | More muscle produces more creatinine, so the estimate understates filtration | Bodybuilders and strength athletes can look worse on paper than their kidneys are |
| Very low muscle mass, amputation or wasting illness | Too little creatinine is produced for the equation’s assumptions to hold | Estimates can overstate function; confirmatory testing matters more here |
| Rapidly changing kidney function | The equation assumes a steady creatinine; in acute injury the blood level lags behind the kidneys | During acute kidney injury every creatinine-based estimate describes where the kidneys were, not where they are |
| Pregnancy | Filtration rises and body composition changes in ways the equation never modelled | Standard adult equations do not apply; pregnancy-specific assessment is needed |
| Severe kidney impairment | Tubular secretion of creatinine grows proportionally as filtration falls, inflating clearance relative to true filtration | At low ranges the estimate increasingly overstates true filtration |
Two further limits are worth naming because they affect ordinary users, not only extreme cases. First, creatinine itself is noisy. A large meat meal, creatine supplements, heavy exercise with muscle breakdown, dehydration and several common medicines can all move creatinine without any change in the kidneys. A single estimate is therefore a snapshot of a moving target, and chronic kidney disease is defined by persistence over at least three months, with repeat blood tests and a urine check for albumin, not by one calculation. Second, at the extremes of body size the weight problem from the previous section returns in full force: the equation treats every kilogram as muscle, so it overstates clearance in obesity when fed actual weight and understates it when fed ideal weight alone. The honest response, used in the literature, is to report a range bounded by the ideal-weight and actual-weight clearances and to let the clinical question decide where inside that range to reason from, rather than pretending one number is exact.
None of this makes the equation useless. It makes it a tool with a known operating envelope: adults with stable kidney function, a steady creatinine, and a body composition somewhere near the population it was derived from. Inside that envelope it is fast, transparent and, crucially, comparable with the labelling that still governs most prescribing. Outside that envelope, the right move is not a better calculator but a different kind of evidence: repeat testing over time, a urine albumin check, and where the stakes are high or the body is unusual, a cystatin C-based estimate, which depends far less on muscle mass, or a directly measured clearance. The calculator on this page is best used as the starting point for that conversation, with both of its estimates in hand, rather than as the conversation itself.
How to read the two numbers together
A short checklist for the moment after the calculation, when the two figures are on screen and disagree by a few points.
First, check the range, not the decimal. If both estimates land in the same range, as they do on the default example at 74.1 and 69.2, that agreement is the reassuring pattern, and the few points between them are not a discrepancy to resolve. Second, if they straddle a boundary, check the weight basis before anything else: open the Advanced panel, add your height, and see whether the actual, ideal and adjusted clearances spread across the boundary too. A straddle driven by weight is a weight question, not a kidney question, and it is answered by asking which basis the relevant reference specifies. Third, check the creatinine itself: is it a steady, recent, fasting-style result, or was it drawn after a heavy meal, a creatine supplement, dehydration or a new medicine? Any of those can shift a single estimate in either direction. Fourth, remember the time dimension. One estimate, however carefully computed, cannot diagnose chronic kidney disease, which requires persistence over months plus, where relevant, evidence of kidney damage such as albumin in the urine. Bring both numbers, the weight spread if there is one, and your medicine list to your clinician or pharmacist, and let them decide what, if anything, needs repeating or confirming.
Measured clearance: the 24-hour urine collection, step by step
The estimate on this page comes from a formula applied to one blood result. A 24-hour urine collection measures clearance directly instead: all urine passed over a full day is collected, the creatinine concentration in that urine is measured, and the total amount excreted is divided by the blood concentration and the time. The formula is clearance in mL/min equals urine creatinine concentration times total urine volume, divided by serum creatinine times 1,440, the number of minutes in a day, with both concentrations in the same units. A worked example: urine creatinine 80 mg/dL, total volume 1,500 mL, serum creatinine 1.0 mg/dL, gives 80 times 1,500, which is 120,000, divided by 1.0 times 1,440, which is 1,440, giving 83.3 mL/min.
The measurement is only as good as the collection. A missed void, an extra void from outside the 24 hours, or a collection that ran short or long all move the result, because the volume term carries the whole day’s output. Laboratories check completeness against the expected daily creatinine excretion for the person’s muscle mass, and an incomplete collection is usually repeated rather than corrected. That is also why measured and estimated clearance can disagree: the formula estimate assumes an average collection and average muscle mass, while the measured figure carries the collection’s own errors. Where the two disagree, the clinician or pharmacist decides which to trust, usually by repeating the collection or the blood test, and neither figure on its own diagnoses kidney disease. General information only; discuss any result with your clinician.
Reading a creatinine level: units, muscle, and one number
Serum creatinine is a concentration, usually reported in mg/dL in the United States or in micromol/L elsewhere, and the number only means something with the person attached. Creatinine comes from muscle, so a muscular person makes more of it and a person with little muscle makes less, and the same blood concentration can sit alongside very different kidney function in the two cases. That is why clearance formulas take age, sex, and weight into account, and why a creatinine that looks normal can still accompany reduced function in an older adult with low muscle mass, as the FAQ on this page explains. A meat-heavy meal and creatine supplements can also raise a single result, which is one more reason a lone reading is never the whole story.
Read a creatinine result as a trend, not a verdict. A rising series over months, a result that stays high on repeat testing, or a high result alongside albumin in the urine, each carry more weight than any single number, and kidney disease is defined by persistence over time plus evidence of damage, not by one laboratory value. Keep the units straight when comparing results from different laboratories, bring the full medicine list, since several common medicines shift creatinine without changing kidney function, and let the clinician decide whether the number needs repeating, confirming with another estimate, or following up at all. This page estimates; it does not diagnose.
Creatinine clearance questions, answered
Which formula, which weight, and what a low number actually means.
Creatinine clearance or eGFR — which number matters?
Both estimate the same filtering job from the same blood test, and each rules a different world. Creatinine clearance from Cockcroft-Gault is what most medicine labels and pharmacy systems use to adjust doses, so it decides how much of a drug someone with reduced kidney function receives. eGFR from CKD-EPI is what lab reports print automatically and what kidney-disease staging is built on. They differ because they were built differently: clearance uses your weight and comes out in plain mL/min, while eGFR ignores weight and is normalised to a standard body size of 1.73 m².
Why is there a 0.85 factor for women?
Creatinine comes from muscle, and on average women carry less muscle per kilogram of body weight than men. When Cockcroft and Gault checked their formula against measured clearance, the unadjusted version overestimated women’s results by roughly 15% — the same blood creatinine level generally means less muscle producing it, not better kidneys hiding it. The formula therefore multiplies a woman’s result by 0.85 to bring the estimate in line with what was actually measured.
My creatinine is in µmol/L — how do I convert it?
Divide by 88.4 — or simply switch the unit selector next to the creatinine box and type your number as printed. A result of 106 µmol/L, typical on reports from Europe, Canada, Australia and most of the world outside the US, is the same blood level as 1.2 mg/dL. The formulas themselves only work in mg/dL, so the calculator converts behind the scenes and shows you both versions of your number.
Why does clearance fall with age if my creatinine never changes?
Because of the (140 − age) term — and it reflects something real. Kidney filtering capacity genuinely declines with age, and so does the muscle mass that produces creatinine. A creatinine of 1.2 mg/dL at age 30 usually means brisk filtering by a muscular body; the same 1.2 at 75 can hide much weaker kidneys behind much less muscle. That is the entire reason age sits inside the formula: the blood number alone cannot tell those two people apart.
My result looks low — what should I do?
Treat it as a prompt, not a verdict. An estimate under 60 is the zone clinicians watch for chronic kidney disease — but only when it persists, which is why guidelines ask for a repeat test over at least three months before anyone uses the word diagnosis. Creatinine swings with hydration, a large meat meal, creatine supplements and some medicines, so a single figure can mislead in either direction. The right move is an appointment: bring the result, ask for a repeat test and a urine check, and review your medicines. Never change or stop a prescribed dose because of a calculator — dose adjustments for kidney function are exactly what pharmacists and prescribers are for.
Actual, ideal or adjusted weight — which should I pick?
Actual weight is the classic default and what most situations assume — start there. The alternatives exist because fat tissue produces very little creatinine: at high body weights, actual weight can flatter the clearance. Ideal body weight (Devine) strips the estimate back to the lean frame, and adjusted body weight — ideal plus 40% of the difference — is the compromise many dosing references prefer for people with obesity. Add your height and this page shows all three so you can see the spread. If the spread crosses a range boundary, that is a conversation for your prescriber, not a coin to flip on your own.
For drug dosing, do pharmacists use CrCl or eGFR?
Historically, most medicine labels and pharmacy systems use Cockcroft-Gault creatinine clearance in mL/min, because the dosing studies behind those labels used that equation. Newer guidance points the other way: the United States Food and Drug Administration issued guidance in 2024 recommending eGFR-based assessment for pharmacokinetic studies in renal impairment, and a National Kidney Foundation consensus the same year supported moving medication-related decisions toward race-free eGFR equations. Until labels are rewritten, the safe statement is that the two systems are in transition, and the figure that matters for a specific medicine is the one its own label specifies. This page shows both figures so you can see them side by side, and it never recommends a dose: which figure applies, and what dose follows from it, is a question for your prescriber or pharmacist.
How is adjusted body weight worked out?
Adjusted body weight = ideal body weight + 0.4 × (actual weight − ideal body weight), where ideal body weight comes from the Devine formula: 50 kg for a man or 45.5 kg for a woman, plus 2.3 kg per inch of height over five feet. Take the worked example on this page: a 60-year-old man, 70 inches tall and 110 kg, has an ideal weight of 73.0 kg and an adjusted weight of 73.0 + 0.4 × (110 − 73.0) = 87.8 kg. His clearance falls from 101.9 mL/min on actual weight to 81.3 mL/min on adjusted weight, and to 67.6 mL/min on ideal weight. Adjusted weight is meaningful only when actual weight exceeds ideal weight; when actual weight is below ideal weight, actual weight is the usual choice.
Why do CrCl and eGFR disagree most in very heavy or very muscular people?
Because only one of the two equations looks at body size at all. Cockcroft-Gault multiplies by weight, so every extra kilogram raises the estimate, whether that kilogram is muscle that produces creatinine or fat that mostly does not. CKD-EPI eGFR ignores weight and reports filtration per 1.73 m² of standard body size, so it does not move with weight in either direction. In a very heavy person the weight-based figure tends to run high and the normalised figure can look low by comparison; in a very muscular person the opposite pattern appears, because abundant muscle raises creatinine and depresses both estimates relative to true filtration. De-indexing the eGFR, by multiplying it by the person’s body surface area and dividing by 1.73, puts both figures back into absolute mL/min and often closes much of the gap.
Can creatinine look normal while kidney function is reduced in an older adult?
Yes, and this is one of the most important traps in kidney numbers. Creatinine comes from muscle, and muscle mass falls with age, so an older adult can have a lower creatinine for the same level of kidney function as a younger person. The arithmetic on this page shows it directly: a man weighing 80 kg with a creatinine of 1.2 mg/dL has a Cockcroft-Gault clearance of 101.9 mL/min at age 30 but only 55.6 mL/min at age 80, with the identical blood result. A creatinine inside the laboratory reference range therefore cannot by itself reassure an older adult. What matters is the age-adjusted estimate, repeated over time, together with a urine check for albumin and a review of medicines and other conditions, all with a clinician.
How is creatinine clearance calculated from a 24-hour urine collection?
Clearance in mL/min equals urine creatinine concentration times total urine volume, divided by serum creatinine times 1,440 minutes, with both concentrations in the same units. For example, 80 mg/dL times 1,500 mL, divided by 1.0 mg/dL times 1,440, gives 83.3 mL/min. The collection must cover a full 24 hours: a missed void makes the result unreliable, and laboratories check completeness before reporting it.
Why does measured clearance differ from the Cockcroft-Gault estimate?
Because one is measured and the other is assumed. The 24-hour collection carries the errors of the collection itself, a missed void or a wrong duration moves it directly, while Cockcroft-Gault assumes average muscle mass and an average relationship between creatinine, age, sex, and weight. The two disagree most where muscle mass is unusual, very high or very low, or where the collection was incomplete. A clinician or pharmacist decides which figure to use, usually after a repeat.
Can diet or supplements change my creatinine result?
Yes, a single result can move. A meat-heavy meal and creatine supplements can raise serum creatinine, and muscle mass itself sets how much creatinine the body makes, so the same kidney function gives different creatinine levels in different people. Hydration and some medicines also shift the number. That is why results are read as trends, repeated where they matter, and interpreted with the medicine list in view, by a clinician.
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