Age Calculator
Exact age in years, months and days, plus weeks, total days, and corrected age for babies born early.
Age Calculator: Your Child’s Exact Age in Years, Months and Days
Put in your child’s date of birth and you’ll get their age in years, months and days, along with the totals people keep asking for: months, weeks, days old.
One thing before you hit calculate. If you’re filling in a nursery form or a health visitor record or paperwork for a developmental assessment, change the second date from today to the date of that appointment. A form you complete on Monday for a Thursday assessment is already three days out, and on a norm-referenced test three days is sometimes enough to move a child into a different age band.
Exact to the day. Free, and nothing to sign up for.
Child Age Calculator
Enter a date of birth and get the exact age in years, months and days, plus the milestones and check ups that come next.
How it works
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1
Enter the date of birth
Type the day, month and year. The fields move along on their own as you go, so it takes a couple of seconds on a phone.
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2
Set the date you are measuring to
It defaults to today. Change it to the day of an assessment, a school cut off or a clinic visit and the age is worked out for that date instead.
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3
Read the age and what comes next
You get the exact age in years, months and days, the totals in months, weeks and days, corrected age if the baby arrived early, the next routine check up, and an illustrated milestone list for that age.
Ages and stages, and why the exact number matters
Nobody asks a forty year old how many months old they are. For children the months are the whole point, because the gap between a child of 24 months and one of 30 months is enormous and the gap between 40 and 40 and a half is nothing at all. Here is roughly what each stage looks like and which number people use for it.
Birth to 28 days
Newborn
Age gets counted in days at this stage because so much changes week to week. Feeding, weight and sleep are what most checks focus on.
1 to 12 months
Infant
Age in months is the number that matters here. Head control, sitting, babbling and first words all get tracked against it.
1 to 3 years
Toddler
Walking, talking and a lot of opinions. Milestone ranges are wide at this stage, so two children the same age can look very different.
3 to 5 years
Preschooler
Sentences get longer, play gets social, and exact age starts to matter for school entry and for scoring assessments.
5 to 12 years
School age
Yearly check ups, and age in years and months for anything to do with school placement or standardised testing.
12 to 18 years
Adolescent
Growth spurts, puberty and mental health take over the yearly visit. Exact age still matters for vaccine timing.
Corrected age, for babies who arrived early
A baby born at 32 weeks arrived eight weeks before their due date. At six months old their body and brain have had roughly four months of the development a baby born at term would have had, so four months is the age you compare them against. That is corrected age, and using it stops a perfectly healthy preterm baby from looking behind on every chart they touch.
Turn on the born early option above and the calculator shows both numbers side by side. Most clinicians correct until around two years and then stop, because by then the difference has usually washed out.
Questions people ask
What is chronological age?
Chronological age is simply how long someone has been alive, counted from the date of birth to a chosen date. For children it is written as years, months and days rather than rounded to the nearest birthday, because a few months either way changes what you should expect from a two year old.
Why does a child age calculator matter more than one for adults?
Almost everything in early childhood is scored against exact age. Growth charts, vaccine timing, developmental milestones and standardised assessments all use age in months and days. Getting it wrong by even a month can push a score into a different band, so people who work with children calculate it rather than estimate it.
How do you calculate a child age in years, months and days?
You subtract the date of birth from the test date one piece at a time, starting with days. If the day of birth is later in the month than the test day, you borrow a month and add its days on. Then you do the same with months, borrowing a year if you need to. This calculator does that for you and shows the working in plain language.
Does it handle leap years?
Yes. The maths runs on real calendar dates, so 29 February and every leap year in between are counted properly. The totals in days and weeks are exact rather than approximate.
What is corrected age, and when should I use it?
Corrected age adjusts for a baby born before 40 weeks. You take the number of weeks the baby arrived early and subtract that from their chronological age. A baby born eight weeks early who is six months old has a corrected age of four months, which is the age you should judge their development against. Most clinicians correct until about two years, and stop after that.
Which date should I put as the test date?
Whatever date the age needs to be true for. Today if you are just curious, the day you ran an assessment if you are writing it up, or a school cut off date if you are checking eligibility. The calculator does not assume today.
Why do some calculators give a slightly different number of days?
Because of how they borrow days. Real calendar months vary between 28 and 31 days, but a lot of standardised test manuals tell you to borrow a flat 30 days instead. Both are defensible and they can differ by a day or two. This tool uses real calendar months by default and has a setting for the 30 day method if your test manual asks for it.
Is the milestone check a screening test?
No. It is a plain language prompt built around the skills most children show by a given age, so you walk into your next appointment knowing what to ask. It does not produce a score, it does not diagnose anything, and a not yet on one or two items is very common in children who are developing perfectly normally.
My child has not hit a milestone yet. Should I be worried?
Milestone ranges are wide, and children pick things up in different orders. What tends to matter more than a single missed item is a pattern across several areas, or a skill that has gone away after they had it. If something is nagging at you, book the conversation. Nobody has ever been told off for asking too early.
Do you store the date of birth I enter?
No. The calculation runs inside your browser, and the date of birth is never sent anywhere. If you choose to email yourself the summary, only the age band and your email address are recorded.
Nothing you type is saved or sent anywhere. The whole calculation runs in your browser.
What your child’s age result actually means?
Years and months is the format forms want and the one you’ll say out loud at appointments. Total months is what growth charts and milestone guides run on until a child is about two. Total days gets asked for less often, but it’s the only figure nobody can round or fudge.
The years-and-months format catches people out because it isn’t a decimal. Four years and six months is 4;6. Write it down as 4.5 on a test protocol and you’ve recorded a different age, which is common enough that most manuals warn about it in the scoring instructions.
How to calculate a child’s age by hand?
Write the later date above the birth date in three columns, year, month and day, then subtract right to left and borrow whenever a column goes negative.
| Year | Month | Day | |
|---|---|---|---|
| Test date | 2026 | 07 | 30 |
| Date of birth | 2021 | 11 | 14 |
| Age | 4 | 8 | 16 |
Days first: 30 minus 14 is 16. Then the months, where 7 minus 11 goes negative, so you borrow 12 months from the year column. That turns it into 19 minus 11, which is 8, and the year column drops to 2025. Then 2025 minus 2021 is 4. The child is 4 years, 8 months and 16 days old, written 4;8 on a form.
Two rules travel with this method. When the day column goes negative you borrow 30 days, not 31 and not 28, because assessment manuals treat a month as 30 days for this particular sum. And you don’t round the days up, so a child who is 8 years, 5 months and 29 days still gets scored as 8;5. A handful of tests set their own convention, and if you’re working from a manual, the manual wins.
Chronological age vs corrected age for babies born early
Chronological age counts from the day a baby was born. Corrected age counts from the day they were due. For a baby who arrived before 37 weeks, those two numbers describe quite different babies for the first couple of years.
Work out how many weeks early the baby came, then take that off the chronological age. A baby born at 30 weeks was 10 weeks early, so at a chronological age of 6 months, roughly 26 weeks, the corrected age is 16 weeks. Call it three and a half months.
Growth charts, milestone checklists and most early assessments should be using the corrected figure for that baby. Common practice is to keep correcting until around age two, and some clinics carry on to three if the baby was born before 28 weeks. Worth asking which one your clinic is working from, because it changes what “on track” is supposed to look like, and nobody volunteers it.
Chronological age vs developmental age
Chronological age is how long a child has been alive. Developmental age, sometimes called an age equivalent, describes skill level: the age at which that performance would be typical.
The two come apart in both directions, often. A five-year-old with a chronological age of 5;2 might come back with a language age equivalent of 3;6, and yes, that gap is worth following up. But an age equivalent isn’t really a score. One extra raw point can shift it by months, which is why reports lean on standard scores and percentiles instead, and why a decent assessor will tell you not to read too much into that line of the report.
Baby age chart: weeks, months and days old
Parents count in weeks first, then months, then years, and the handover points are vague enough that forms and relatives will ask you for all three anyway. Here’s roughly where they line up.
| Age in weeks | Roughly | Days old |
|---|---|---|
| 4 weeks | 1 month | 28 |
| 8 weeks | 2 months | 56 |
| 13 weeks | 3 months | 91 |
| 17 weeks | 4 months | 119 |
| 22 weeks | 5 months | 154 |
| 26 weeks | 6 months | 182 |
| 30 weeks | 7 months | 210 |
| 35 weeks | 8 months | 245 |
| 39 weeks | 9 months | 273 |
| 43 weeks | 10 months | 301 |
| 48 weeks | 11 months | 336 |
| 52 weeks | 12 months | 364 |
Calendar months run 30 or 31 days and a month of weeks is 28, so the two drift apart across the year. By the end of it the gap is a full day. 52 weeks falls the day before a first birthday, not on it.
Most clinics count in weeks up to about three months, months up to two years, then years. So if a form wants age in months and your baby is 11 weeks old, the answer is 2 months, even though it feels like you’re short-changing them.
Why exact age matters for developmental testing
Norm-referenced assessments turn a raw score into a standard score using tables split into age bands, often three or four months wide. Two children with identical raw scores can land on different standard scores because one of them sits a day the other side of a band boundary. That’s why speech therapists, occupational therapists, educational psychologists and early years teams work the age out to the day rather than estimating it.
A few habits keep this clean. Use the date of the assessment rather than the date you’re scoring the protocol, which might be a week later. Write it as years;months, so 4;8, never 4.67 and never “nearly five”. If the child is under two and was born early, put that on the protocol along with a note of which age you used.
All of that gives way to the manual. Wechsler scales, Brigance, ASQ and the Pearson-published assessments each set out their own age instructions in the front matter, and they aren’t identical.
Five things that throw a child’s age off by a month
- Filling the form on the wrong day: Today’s date instead of the appointment date.
- Rounding the days up: 29 days still isn’t a month, however close it feels.
- Date format: 03/07 is 3 July in the UK and 7 March in the US, and this accounts for a decent share of the “your calculator is broken” emails.
- Ignoring prematurity: For a baby born at 32 weeks, chronological age overstates them by two months.
- Reading 2.9 years as 2 years 9 months: It isn’t, and the difference is bigger than it looks.