Baby Age Calculator – Your Baby’s Age in Weeks, Months and Days
Babies are not measured in years — they are measured in weeks, then in months and days.
When was your baby born?
🔒 Everything is calculated in your browser — your baby’s dates never leave your device.
Your baby’s age
🎂 Coming up
Next milestone: turns 3 months old on 15 Nov 2026 — in 24 days. First birthday: 15 Aug 2027, with 297 days to go.
| Breakdown | Value |
|---|---|
| Date of birth | 15 Aug 2026 |
| Age as of | 22 Oct 2026 |
| In months and days | 2 months, 7 days |
| In years, months and days | 0 years, 2 months, 7 days |
| In weeks and days | 9 weeks, 5 days |
| Total days old | 68 |
| Next monthly milestone | 3 months on 15 Nov 2026 |
| Next birthday | 15 Aug 2027 (297 days away) |
Why weeks? In the first months a baby changes week to week, and months are uneven — 28 to 31 days — so weeks are the honest unit early on. Your baby is 9 weeks and 5 days old, which the calendar calls 2 months and 7 days.
The first year, month by month
Every monthly milestone of the first year, with its exact date. The list rebuilds itself for your baby’s birthday — milestones already reached are ticked, and the next one is highlighted.
Monthly milestones fall on the same date each month — a baby born on the 15th turns 3 months on the 15th, three months later. When a month is too short for the date (a baby born on 31 January), the milestone lands on that month’s last day instead — 28 February — and the count carries on from there.
The dates around a baby
Birthdays are one date in a whole calendar of them — these are the tools parents pair with this one.
Babies are not measured in years — they are measured in weeks, then in months and days. Enter your baby’s date of birth and see the exact age the way parents and pediatricians say it: months and days, total weeks, total days, and the next monthly milestone with the date it lands on.
Key takeaways
- One birth date, counted three honest ways — by the calendar, by the week and by the day.
- Every monthly milestone of the first year, with its exact date.
- Why the early months are counted in weeks — and the adjustment doctors make for babies who arrived early.
Contents
How it works
One birth date, counted three honest ways — by the calendar, by the week and by the day.
Count whole calendar months
A baby turns 1 month old on the same date the next month — born on 15 August, one month old on 15 September. The calculator counts how many of those month-dates have fully passed, then counts the leftover days one by one.
Count every day, then make weeks
Separately, it counts the total days since birth and divides by 7: that is the weeks-and-days figure nurses and baby books use, the most precise of the three in the early months.
Mark what comes next
Finally it looks ahead: the next monthly milestone (the next month-date, with its calendar date) and the next birthday, with a day countdown to each — the two dates parents actually plan around.
The math behind the example
Step 1 — whole months. Born 15 Aug 2026, checked on 22 Oct 2026. The month-dates that have fully passed are 15 September (1 month) and 15 October (2 months) — so the baby is 2 whole months old, and the count anchors on 15 Oct 2026.
Step 2 — the leftover days. From the anchor, 15 October, to the check date, 22 October, is exactly 7 days. The age in months and days: 2 months, 7 days.
Step 3 — days and weeks. Counting every day from 15 August to 22 October gives 68 days in total. Divided by 7, that is 9 full weeks with 5 days left over: 9 weeks, 5 days — the same age, in the unit the early months are usually counted in.
Step 4 — what comes next. The next month-date is 15 Nov 2026, when the baby turns 3 months old; the first birthday is 15 Aug 2027, which is 297 days after the check date.
Two things parents ask about baby ages
Why the early months are counted in weeks — and the adjustment doctors make for babies who arrived early.
A newborn changes visibly from one week to the next — feeding, waking, focusing — so the first stretch of life is naturally counted in weeks, and health visitors and baby books do the same. Weeks are also the only honest unit early on, because months refuse to sit still: they run 28 to 31 days, so “one month old” can mean anything from 28 to 31 days depending on where the birthday falls.
The mismatch is worth memorising: a month is not 4 weeks. Twelve months of 4 weeks would make a 48-week year, but a real year has 52 weeks — the average month is about 4.35 weeks (365 ÷ 12 ÷ 7 ≈ 4.35). That is why a baby who is 16 weeks old is not quite 4 months old yet, and why this calculator counts months by the calendar and weeks by sevens, separately, instead of converting one into the other.
This calculator gives the chronological age — the time since the day your baby was born. For babies born before their due date, doctors and health visitors also track a second number, the corrected age (sometimes called adjusted age): the age counted from the due date instead of the birth date. Developmental milestones are usually judged against the corrected age in the first couple of years, so a baby born 6 weeks early is expected to reach milestones roughly 6 weeks behind their chronological age — and that is normal, not a delay.
You can see the corrected age on this page too: enter the due date in the “Age on a date” thinking — simply put the due date in as the date of birth, and the months, weeks and days it shows are the corrected age for today. None of this replaces your pediatrician’s judgement; it just explains the two numbers you may hear at appointments.
Baby age questions, answered
Weeks versus months, month-end birthdays, and checking an age on a date that has not happened yet.
Why do people count a baby’s age in weeks?
Because in the first months, a week is a long time in a baby’s life — feeding, sleep and development all move week by week — and because months are uneven, running 28 to 31 days. Saying “9 weeks old” is exact; saying “about 2 months” is not. Most parents switch to months once the weeks pass the teens, which is why this calculator shows both: weeks and days alongside months and days.
How are the months in a baby’s age calculated?
By the calendar, the same way birthdays work. A baby turns 1 month old on the same date in the next month — born on 15 August, one month old on 15 September — however many days that month happens to have. This calculator counts how many of those month-dates have fully passed, then counts the remaining days. So a baby born on 15 Aug 2026 is, on 22 Oct 2026, exactly 2 months and 7 days old (68 days, or 9 weeks and 5 days, in total).
My baby was born on the 31st — when do the monthly milestones fall?
On the last day of any month too short to hold the date. A baby born on 31 January turns 1 month old on 28 February (the last day of February), then 2 months on 31 March. The count itself is never short-changed: the calculator anchors each month on the birthday date, clamped to the end of shorter months, so a baby born on 31 Jan 2026 is 1 month and 1 day old on 1 Mar 2026 — the full month through the end of February, plus the extra day.
What is corrected age for a premature baby?
Corrected age (also called adjusted age) counts a premature baby’s age from their due date instead of their birth date. It is the number doctors use when judging developmental milestones for roughly the first two years, because a baby born early has had less time to develop. This calculator shows chronological age from the birth date; to see the corrected age, enter the due date as the date of birth and read the result the same way. Always follow your pediatrician’s guidance for your own baby.
Can I check how old my baby will be on a future date?
Yes — that is what the “Age on a date” mode is for. Enter the birth date and any other date — a school or nursery cut-off, a vaccination appointment, next Christmas — and the calculator shows the exact age on that day, in months and days, weeks, and total days. It works for dates in the past as well, so you can also check how old your baby was when a photo was taken or a milestone was reached.
How is this different from a regular age calculator?
A general age calculator leads with years, which is the wrong unit for a baby — nobody calls a newborn “0 years old”. This one leads with months and days, adds the weeks-and-days figure parents and baby books actually use, labels the stage (newborn, infant, toddler, preschooler), and looks ahead to the next monthly milestone and the next birthday with their dates. The underlying calendar math is the same; the presentation is built for the first years of life.
More calculators for the early years
The rest of the baby-dates toolkit — conception to countdowns.
Age Calculator
Exact age for anyone, in years, months and days.
→ 🎂Birthday Calculator
Next-birthday countdowns and day milestones.
→ 🤰Pregnancy Calculator
Due dates and pregnancy weeks.
→ 🗓️Conception Calculator
Work back from a due date or birth date.
→ 📅Date Calculator
Add or subtract days from any date.
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