Treasury Bond Calculator – Series I Bond Value and Growth
A Series I savings bond is the US Treasury’s inflation-proof loan to yourself: you lend the government money, and in return your savings grow at a rate that resets with inflation every six months. Type in what you put in and the rate, and this page shows what the bond is worth year by year — including exactly what you would receive if you cashed in early, after the three-month penalty comes off.
Your I bond
Build a composite rate yourself
Composite rate: 4.26% — from a 0.90% fixed rate and 1.67% semiannual inflation (the May 2026 announcement).
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The growth
The money, line by line
How to read this
At 5 years the bond is past the penalty window, so the value above is the full amount you would receive — nothing is held back. Remember that this projection holds today’s rate still for the whole period; a real I bond’s rate resets every 6 months, so your actual path will step up and down with inflation.
- Bond value = purchase × (1 + composite rate ÷ 2) raised to (2 × years) — interest compounds every six months, the Treasury’s way.
- The composite rate is two parts, a fixed rate plus twice the semiannual inflation rate, and Treasury stops the combined rate at zero.
- Cash in before five years and the last three months of interest are forfeited; for the first 12 months the money is locked.
- Year by year
- Pairs well with this calculation
- An I bond in three steps
- How the treasury bond calculator works
- Going deeper
- The composite rate, worked from its two parts
- The penalty, year by year, at the pre-filled rate
- I bonds beside EE bonds, and the savings bond calculator
- Tax treatment, in outline only
- Bills, notes, bonds, TIPS, and FRNs: one auction, five instruments
- Savings bonds beside marketables: why the I-bond answers live on their own terms
- Frequently asked questions
Year by year
One row per year: what the bond is worth, how much of that is interest, and what you would actually receive if you cashed in at that point — penalty already taken off where it applies.
| Year | Bond value | Interest so far | If you cash in |
|---|---|---|---|
| 1 | $10,430.54 | $430.54 | $10,321.20 |
| 2 | $10,879.61 | $879.61 | $10,765.56 |
| 3 | $11,348.02 | $1,348.02 | $11,229.06 |
| 4 | $11,836.59 | $1,836.59 | $11,712.51 |
| 5 | $12,346.20 | $2,346.20 | $12,346.20 |
The cash-in column for years 1 to 4 is the bond’s value three months earlier — that is literally what the penalty does: it pays you as if you had cashed in one quarter sooner. From year 5 on, the two columns are the same.
The honest assumption on this page
A real I bond does not keep one rate. Its fixed part is locked for life, but the inflation part — and so the composite rate — is reset every six months, on the anniversary of your purchase. Nobody knows the future resets, so this calculator holds the single rate you enter steady for the entire period. Treat the result as a clean what-if at that rate, not a forecast: over long horizons your real value will land higher or lower depending on the inflation path. The formula, the compounding and the penalty are the Treasury’s real mechanics — only the future rate is unknowable, and no page can fix that.
Pairs well with this calculation
The rest of the safe-money shelf — the general savings bond estimator, and what steady compounding does anywhere else.
An I bond in three steps
Buy it, then wait a year
You buy electronic I bonds at TreasuryDirect, in any amount from $25 up to $10,000 per person per calendar year. For the first 12 months the money is locked — the bond simply cannot be cashed in, emergencies aside. After that you can redeem it at any time, in whole or in part.
The rate resets twice a year
Your rate is a composite: a fixed rate set when you buy and kept for life, plus an inflation rate that follows the Consumer Price Index. Treasury announces new rates every May 1 and November 1, and your bond picks up each new inflation rate on its own six-month anniversaries — so in a high-inflation spell your return climbs, and it falls back when inflation cools.
Interest folds in every 6 months
Interest is earned monthly and compounded semiannually: every six months the interest you have earned is added to the principal, and from then on you earn interest on the interest too. Hold at least 5 years and every cent of it is yours; leave earlier and the last 3 months of interest stay behind. At 30 years the bond stops earning and reaches final maturity.
How the treasury bond calculator works
bond value = purchase × (1 + composite rate ÷ 2)2 × years
The compounding. Say you put $10,000 into an I bond at a 5.27% composite rate. Every six months the bond earns half the annual rate, 2.635%. After the first six months it is worth $10,000 × 1.02635 = $10,263.50. The second half-year earns on that larger amount: $10,263.50 × 1.02635 = $10,533.94. One year, $533.94 of interest — a little more than a flat 5.27% of $10,000, because the second half-year’s interest itself earned interest. That fold-in, twice a year, is the whole engine of this page.
The penalty. Cash that same bond in at the one-year mark and the Treasury removes the last 3 months of interest. The clean way to see it: you are paid the value the bond had at 9 months, $10,397.84. The penalty is $10,533.94 − $10,397.84 = $136.10 — never any of your principal, only recent interest. From the fifth anniversary onward there is no penalty at all.
The composite rate. The rate itself is built from two announced pieces: composite = fixed rate + 2 × semiannual inflation rate + (fixed rate × semiannual inflation rate). For bonds issued from May to October 2026, TreasuryDirect set a fixed rate of 0.90% and measured semiannual inflation at 1.67%, so the composite is 0.90 + 3.34 + 0.015, which rounds to the announced 4.26%. The little cross-term at the end is the fixed rate earning on the inflation adjustment — small, but it is in the official formula, so it is in this page’s too. Try it in the helper box above the results.
Going deeper
The composite formula has a floor built into it. If inflation runs negative for a six-month stretch — deflation — the inflation part of the formula goes negative and drags the composite down, possibly below the fixed rate. But Treasury stops the combined rate at zero: an I bond can have a six-month period in which it earns nothing, yet it can never lose value from the rate itself. Your principal and every cent of interest already credited stay intact.
That asymmetry is the I bond’s real selling point. In an inflationary spell the rate climbs twice a year to meet prices; in a deflationary spell the worst case is a pause, not a loss. Very few savings products promise both directions of protection at once, which is why the purchase limit, not demand, is what keeps I bonds a niche corner of household savings.
The 12-month lock. For the first year an I bond cannot be redeemed at all (the narrow exception is a declared-disaster waiver). Money you might need within a year does not belong in an I bond, however attractive the rate looks.
The $10,000 cap. Each person can buy up to $10,000 of electronic I bonds per calendar year, per TreasuryDirect account. That cap — not the rate — is why I bonds sit alongside, rather than instead of, other savings.
Taxes. I bond interest is subject to federal income tax but exempt from state and local tax. You can defer the federal tax until you cash in or the bond matures at 30 years, and interest used for qualified higher-education expenses can be partly or fully excluded if you meet the income and ownership rules. None of that changes the growth on this page, which is shown before any tax.
The composite rate, worked from its two parts
The rate on this page is not a single number chosen by the calculator; it is a composite built by the Treasury’s formula from two parts that behave differently. The formula, stated in the FAQ above, is: composite rate equals the fixed rate, plus twice the semiannual inflation rate, plus the fixed rate times the semiannual inflation rate. The fixed rate is set when the bond is issued and never changes for the life of the bond. The inflation rate is reset every six months, from the Consumer Price Index, with Treasury announcing new rates every May 1 and November 1. The page pre-fills 4.26 percent, which is the rate announced on May 1, 2026, for bonds issued from May to October 2026: a fixed rate of 0.90 percent and a semiannual inflation rate of 1.67 percent, combined as 0.90 plus twice 1.67, which is 3.34, plus the cross-term of 0.90 percent times 1.67 percent, which is 0.015 percent, giving 4.255 percent, displayed as 4.26 percent.
The cross-term is the part most explanations skip, and it is worth a sentence because it is the reason the composite is not simply the sum of its parts. The fixed rate applies to the whole bond, and the inflation rate applies twice, once for each half-year, but the inflation adjustment itself also earns the fixed rate, which is what the product term captures. At the pre-filled figures the cross-term is only 0.015 percentage points, small enough to ignore for a rough estimate and large enough to matter for an exact one: omitting it gives 4.24 percent instead of 4.26 percent, and on $10,000 over five years that two-hundredths of a point is worth about $12. The calculator does not omit it, and neither should any hand calculation that claims to reproduce the Treasury’s figure. Note carefully what the pre-filled rate is and is not: it is the announced rate for one issue window, May to October 2026, not a live rate for all bonds, because a bond you already own picks up each new inflation rate on its own six-month anniversaries, so there is never a single live rate that applies to everyone. Enter the rate that applies to your bond’s current period, or use the pre-filled figure as the labelled example it is.
The fixed rate deserves a paragraph of its own, because it is the only part of the return you can lock in. A bond bought when the fixed rate is 0.90 percent keeps that 0.90 percent for thirty years, however inflation moves, while a bond bought when the fixed rate is zero earns only the inflation component, however high inflation runs. That asymmetry is why the fixed rate at purchase matters more than any single inflation announcement: inflation readings come and go twice a year, but the fixed rate compounds for the life of the bond. A buyer comparing two purchase dates should compare their fixed rates first and their inflation components second, because the inflation component of either bond will be replaced within six months, while the fixed rate never will be.
The penalty, year by year, at the pre-filled rate
The year-by-year table on this page already shows what a $10,000 bond at the pre-filled 4.26 percent is worth each year and what you would actually receive if you cashed in, with the penalty already taken off where it applies. The table below isolates the penalty itself, so the cost of leaving early can be seen directly rather than inferred from the gap between two columns. The penalty is the last three months of interest, forfeited on any redemption between one year and five years; before one year there is no redemption at all, and after five years there is no penalty.
| Cash in at | Bond value | You receive | Penalty (interest forfeited) |
|---|---|---|---|
| Year 1 | $10,430.54 | $10,321.20 | $109.34 |
| Year 2 | $10,879.61 | $10,765.56 | $114.05 |
| Year 3 | $11,348.02 | $11,229.06 | $118.96 |
| Year 4 | $11,836.59 | $11,712.51 | $124.08 |
| Year 5 | $12,346.20 | $12,346.20 | $0.00 |
Two features of the penalty are worth noticing. First, it grows with the bond, because three months of interest on a larger balance is a larger sum: $109.34 at year one, rising to $124.08 at year four, even though the rate never changed. Second, it only ever touches interest, never the purchase amount: the cash-in figure at year one, $10,321.20, is still above the $10,000 paid in, because nine months of interest remain after the three forfeited months. The penalty is therefore a reduction in return, not a loss of principal, which is a meaningful distinction for a saver weighing an early exit against holding on. The FAQ above gives the same penalty at a different rate, 5.27 percent, where cashing in $10,000 at one year forfeits $136.10, and the comparison between the two rates shows the same rule: higher rate, larger three-month slice, larger penalty.
The twelve-month lockup deserves equal emphasis, because it is absolute in a way the penalty is not. For the first twelve months the bond simply cannot be redeemed, and a saver who may need the money within a year should not put it in an I bond at all, whatever the rate. The lockup, the penalty window and the thirty-year final maturity together define the shape of the product: money that is unavailable for a year, penalised for early exit until year five, and productive for up to thirty years. A saver whose horizon is shorter than the lockup needs a different product; a saver whose horizon is five years or more never meets the penalty at all, and the only cost of the I bond’s structure for them is the opportunity cost of money that could have earned more elsewhere.
I bonds beside EE bonds, and the savings bond calculator
The FAQ above draws the boundary between this page and the general savings bond calculator, and the boundary is worth restating because the two Treasury products are often confused. This page is I-bond specific: it is built around the composite rate, showing how the fixed rate and the inflation rate combine, and projecting growth year by year at a rate you choose. The savings bond calculator is the general tool: it estimates what a bond you already hold, Series EE or Series I, is worth today, including the EE rule that guarantees an EE bond doubles in value if held for twenty years. The EE doubling rule is the EE bond’s answer to inflation protection: instead of tracking the Consumer Price Index, the Treasury tops an EE bond up to twice its purchase price at twenty years if its regular interest has not already done so.
The practical difference for a buyer is the risk each bond insures against. An I bond insures against inflation: if prices rise, the inflation component rises with them, and the bond’s purchasing power is roughly preserved, whatever happens to market interest rates. An EE bond insures against low rates over a long horizon: if market rates stay low for twenty years, the doubling guarantee provides a floor return of about 3.5 percent a year, compounded, which is the annual rate that doubles money in twenty years. Neither bond can be redeemed in its first year, and both share the five-year penalty window for early redemption, so the choice between them is not about access but about which risk the saver fears more: rising prices, which favour the I bond, or a long period of low nominal rates, which favours the EE bond’s guarantee. A saver who fears both, or who cannot decide, can hold both, within the separate purchase limits that apply to each series.
Purchase limits are the last structural fact to state plainly, because the calculator deliberately accepts larger amounts than the law allows for one person. The legal limit for electronic I bonds is $10,000 per person per calendar year, bought through a TreasuryDirect account, in any amount from $25 upward, as the FAQ above states. The calculator accepts larger amounts so that a household can run a combined projection, or a saver can model a multi-year accumulation, but it flags any amount above the limit rather than silently accepting it as a single purchase. Paper I bonds, bought with a tax refund, are a separate small allowance that this page does not model, and the omission is stated here so that nobody mistakes the electronic limit for the whole story. For a single buyer in a single year, $10,000 electronic is the figure that governs.
Tax treatment, in outline only
I bond interest is taxed at the federal level but not at the state or local level, and the federal tax is deferred until the bond is redeemed or reaches final maturity, rather than being due year by year as the interest accrues. Deferral is a real benefit: a saver in a high tax bracket today who expects a lower bracket in retirement keeps the full interest compounding in the meantime and pays tax only on exit, at the bracket that then applies. The exemption from state and local tax is a second benefit, worth more in high-tax states than in low-tax ones, and it is one reason I bonds compare favourably with bank interest, which is taxed at all levels as it is earned.
There is also an education exclusion, under which interest on I bonds, and on EE bonds, used for qualified higher-education expenses can be excluded from federal income tax, subject to income limits, ownership conditions and other requirements that have changed over time. The exclusion is mentioned here so that savers know it exists, not so that they rely on it: its conditions are specific, including that the bonds must be owned by someone at least 24 years old at issue and that the expenses must be for the owner, a spouse or a dependent, and the income limits phase the benefit out. Nothing in this section is tax advice, and nothing on this page computes a tax figure; a saver planning around deferral or the education exclusion should confirm the current rules with a tax professional before buying on the strength of them. The calculator’s job is the pre-tax projection, and the tax treatment is a separate calculation that depends on the saver’s own circumstances.
Bills, notes, bonds, TIPS, and FRNs: one auction, five instruments
The Treasury sells all its marketable debt the same way. The instruments differ in term and in how they pay.
Treasury bills mature in 4 to 52 weeks, pay no periodic interest, and are sold at a discount: you pay less than face value and receive the full face value at maturity, and the difference is the return. Treasury notes mature in 2, 3, 5, 7 or 10 years and Treasury bonds in 20 or 30 years; both pay interest every six months at a coupon rate set at auction, and return the face value at maturity. TIPS (Treasury Inflation-Protected Securities) adjust their principal with inflation, so both the coupon payments and the maturity value rise with prices. FRNs (floating-rate notes) pay interest that resets with the discount rate of the most recent 13-week bill auction. All five are sold through the same auction process, in $100 minimums and $100 increments for non-competitive bids.
The auction is the price-setting mechanism, and it is worth understanding because it explains why no calculator can quote you a live yield. Competitive bidders — banks, dealers and institutions — state the rate or yield they will accept; non-competitive bidders, which is how individuals buy through TreasuryDirect, accept whatever rate the auction determines and are guaranteed their securities up to $10 million per auction. All successful bidders receive the same price, set by the highest accepted competitive bid. The yield you actually earn is therefore decided at the auction, not when you type a number into a calculator — which is why this page works from a rate you enter, and never presents an entered rate as the market rate.
Savings bonds beside marketables: why the I-bond answers live on their own terms
The calculator on this page models an I bond. Marketable Treasuries behave differently in the ways that matter most.
Savings bonds — Series I and Series EE — are non-marketable: you buy them from the government through TreasuryDirect (from $25), hold them with the government, and redeem them with the government. You cannot sell them to another investor, and their value never falls with market interest rates. Marketable bills, notes and bonds can be bought and sold on the secondary market after the auction, so their market price moves every day as interest rates move: a bond bought at par can be worth less than par before maturity if rates have risen, and more if rates have fallen. Holding to maturity removes that price risk for both kinds; selling early does not.
The tax treatment differs in outline too. Interest on Treasury securities is exempt from state and local income tax, though it is subject to federal income tax — one of the few genuine tax advantages of holding Treasuries directly. I-bond interest can be deferred until redemption, and in some cases excluded when used for education, under rules with income limits. Those are outlines only: the calculator on this page is an I-bond growth model with a composite rate you enter, and the article linked from this page explains the wider family, the auction, and the differences without quoting a live yield for any of them.
Frequently asked questions
What does this treasury bond calculator do?
It projects the value of a Series I savings bond from three things you enter: the purchase amount, a composite rate, and how long you hold it. Interest is compounded every six months, the Treasury’s way, and the page shows the value year by year together with what you would actually receive if you cashed in — which, before five years, is less, because the last three months of interest are forfeited.
How is the I bond composite rate calculated?
By the Treasury’s formula: composite rate = fixed rate + (2 × semiannual inflation rate) + (fixed rate × semiannual inflation rate). The fixed rate is set when your bond is issued and never changes; the inflation rate is reset every May 1 and November 1 from the Consumer Price Index. For bonds issued from May to October 2026, a fixed rate of 0.90% and semiannual inflation of 1.67% combine to the announced 4.26%. The helper on this page lets you combine any fixed rate and inflation reading the same way.
Is the rate on this page the live I bond rate?
No — and be wary of any page that claims to show one inside a calculator. Rates are announced by TreasuryDirect every May 1 and November 1, and the rate on a bond you already own resets every six months from its own issue date, so there is never a single live rate that applies to everyone. This page pre-fills 4.26%, the rate announced on May 1, 2026, for bonds issued from May to October 2026, purely as a labelled starting example. Enter the rate for your own bond, or any what-if rate, and the projection follows it.
What happens if I cash in an I bond early?
During the first 12 months you cannot cash in at all. Between one year and five years you can redeem, but you forfeit the last three months of interest — on a $10,000 bond at 5.27% cashed in at one year, that is $136.10, and the penalty only ever touches interest, never your purchase amount. After five years there is no penalty, and the bond keeps earning until it reaches final maturity at 30 years.
How much can I put into I bonds?
Up to $10,000 in electronic I bonds per person per calendar year, bought through a TreasuryDirect account, in any amount from $25 upward to the penny. The calculator accepts larger amounts so you can run what-if projections — for a household total across several people, say — but the legal purchase limit for one person in one year is $10,000, and this page flags any amount above it rather than blocking it.
How is this different from the savings bond calculator?
The CalcFolk savings bond calculator is the general tool: it estimates what a bond you already hold — Series EE or Series I — is worth today, including the EE rule that guarantees the bond doubles at 20 years. This page is I-bond specific: it is built around the composite rate itself, showing how the fixed rate and the inflation rate combine, projecting growth year by year at a rate you choose, and pricing the early-redemption penalty at every horizon. Use the other page to value an existing bond; use this one to understand and project an I bond.
What happens to my rate when Treasury announces new rates?
Only the inflation part changes, and only on your bond’s own schedule. Treasury announces new rates every May 1 and November 1, but your bond picks up each new inflation rate on its own six-month anniversaries from its issue date, not on the announcement date itself. A bond issued in August, for example, resets in February and August, whatever the May and November announcements say. The fixed rate from your issue date never changes. That is why the calculator holds a single rate steady as a what-if: a real bond’s path steps up and down with inflation every six months, and no single entered rate can describe its whole life, only the current period or a chosen assumption.
Should I buy before or after a rate announcement?
Buy for the fixed rate, not for the announcement. The inflation component you will earn first is the one in force for your issue window, and it will be replaced within six months, while the fixed rate you lock in lasts for the life of the bond. A buyer who waits for a higher inflation announcement gains at most six months of a higher inflation component and risks a lower fixed rate at the next issue window, or a lower inflation component after that. The decision that matters most is the fixed rate on offer at purchase, followed by whether the money can stay untouched for at least a year, given the twelve-month lockup. Timing a purchase around an announcement date is timing around the least durable part of the return.
Can I buy I bonds for my children?
Yes, within the purchase limits, through a TreasuryDirect account, where a minor’s bonds are held in a custodial account linked to an adult’s account. Each person has their own $10,000 annual electronic limit, so a household’s total capacity grows with the number of people it buys for, which is why the calculator accepts amounts above $10,000 for household projections while flagging the single-person limit. Paper I bonds bought with a tax refund are a separate small allowance that this page does not model. Custodial ownership, tax reporting and the education exclusion all have their own rules for bonds bought for a minor, so confirm the current TreasuryDirect arrangements before buying for someone else’s benefit.
What if inflation turns negative?
The composite rate cannot go below zero. If the semiannual inflation rate is negative enough to pull the composite below zero, Treasury floors the composite at zero for that period, so the bond earns nothing for those six months but never loses value from the rate itself. The fixed rate softens the effect: a bond with a positive fixed rate needs a larger deflationary reading to reach the floor than a bond with a zero fixed rate. Deflation is also why the composite formula’s cross-term matters in the other direction: with a negative inflation rate the product term is negative too, pulling the composite down slightly faster than the simple sum of the parts would suggest, until the zero floor catches it.
Can I lose money on a Treasury bond?
If you hold it to maturity, no — the Treasury pays the face value at maturity, and the coupons along the way, backed by the full faith and credit of the United States. If you sell before maturity, yes: the market price depends on current interest rates, so a bond sold when rates have risen since issue will fetch less than you paid, and one sold when rates have fallen will fetch more. That price risk is the difference between a marketable bond and a savings bond, whose redemption value never falls below what you paid plus accrued interest. Decide before buying whether you can hold to maturity; if you cannot, the price at sale is a market outcome, not a promise.
Are Treasury interest payments taxed by states?
No. Interest on Treasury bills, notes, bonds, TIPS and FRNs is exempt from state and local income tax, although it is subject to federal income tax. That exemption is a real advantage in high-tax states, and it is one reason Treasury yields are often compared with taxable yields on an after-tax basis rather than head-to-head. Savings-bond interest follows the same state exemption, with federal tax generally deferred until redemption for I and EE bonds. State tax rules for other federal obligations differ, so the exemption described here is specific to Treasury securities.
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