Age Calculator
Calculate your exact age in years, months and days from your date of birth. Also shows total months, weeks, days, hours and the countdown to your next birthday.
Everything runs in your browser, your date of birth is never sent anywhere.
Choose your date of birth and press Calculate Age.
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Almost everyone can say how old they are in years. Far fewer can say how old they are in years, months and days, and the reason is that the calendar refuses to cooperate. Months are 28, 29, 30 or 31 days long, February changes length every fourth year, and there is no single agreed way to turn a run of days into a run of months.
This calculator resolves that the same way official paperwork does. It counts whole calendar years first, then whole calendar months, then whatever days are left over. Nothing is averaged and nothing is rounded. The consequence is worth stating plainly: the months figure you see here is a count of birthdays-of-the-month that have passed, not a day total divided by 30.
A worked example
Suppose you were born on 31 January 1998 and today is 18 August 2026.
- Count the full years: 31 January 1998 to 31 January 2026 is 28 years.
- Count the full months from there: 31 January to 30 June is five months, but 31 July does exist, so we reach 31 July and stop. That is 6 months.
- Count the leftover days: 31 July to 18 August is 18 days.
Your age is 28 years, 6 months and 18 days. A tool that treats a month as thirty days would report 28 years, 6 months and 20 days for the same birthday, a small error, but a real one, and it grows the further back the birth date sits.
The 31st is where most implementations quietly disagree. If you were born on the 31st and the month you land in only has 30 days, the month cannot complete, so we hold at 30 days elapsed and carry the remainder into the day count. Some calculators instead clamp the birthday to the last day of the short month, which advances the month counter a day early. Both behaviours appear in shipped software; ours is the conservative one, and it is the one that matches how a registrar reads a date.
The result panel gives you five views of the same span. They are not five competing answers, they are one age expressed in five units, and each one is the right choice for a different job.
| Field | What it counts | Best used for |
|---|---|---|
| Years, months, days | Whole calendar units, in that order | Forms, applications, medical records |
| Total months | Every complete calendar month lived | Infant and toddler milestones, subscriptions |
| Total weeks | Whole seven-day blocks since birth | Newborn charts, training and recovery plans |
| Total days | Real calendar days, leap days included | Round-number celebrations, precise gaps |
| Total hours | Total days × 24 | Curiosity, mostly, but the maths is exact |
The five figures are different views of one span, not five different answers.
One practical note on total months. For a baby, months are the unit that matters, a paediatric growth chart is read in months, not in years and months, which is why the figure is given separately rather than left for you to multiply out. For an adult it is mostly a curiosity, but it is the cleanest way to answer questions like “how many monthly payments have I made since I turned 18”.
Roughly one person in 1,461 is born on a leap day, and they are the only people for whom “when is my birthday” has no single correct answer in three years out of four. The calendar simply does not offer the date.
Two conventions are in use. The 28 February convention says the birthday falls on the last day of February, so a leap-day baby turns 18 on 28 February 2043. The 1 March convention says the birthday falls the day after the last day of February that existed in the birth month, so the same person turns 18 on 1 March. Both are defensible; neither is universal.
In practice, software overwhelmingly uses 28 February, because that is what date libraries produce when you clamp an invalid date to the end of the month, and this calculator follows the same convention so its answer matches the systems you are most likely to be filling a form for. But the law is not software. England and Wales, for instance, has authority for treating a person as attaining an age at the start of the day before the anniversary in some statutory contexts, and other jurisdictions specify 1 March outright for licensing and pension purposes.
Mental age arithmetic is fine for a rough figure and unreliable for an exact one. It is worth knowing which shortcut you are using, because each one fails in a specific, predictable way.
Where the mental shortcut is fine
- Working out someone’s age in whole years when you know their birthday has already passed this year, current year minus birth year is exact.
- Sanity-checking a calculator’s output. If a tool tells you a 1998 birth date makes you 31, the year subtraction catches it instantly.
- Comparing two people born in different years, where you only need to know who is older.
- Any context where “about 40” is the answer being asked for, a rough figure honestly labelled is better than a precise figure applied to the wrong question.
Where it goes wrong
- Subtracting years and stopping. The answer is a year too high for anyone whose birthday has not yet arrived this year, that is, for roughly half the population on any given day.
- Treating a month as thirty days. Source of nearly every off-by-one and off-by-two error in hand-worked date maths, because seven months of the year are not thirty days long.
- Multiplying years by 365. Drops one day for every leap year lived through: about five days at age twenty, about ten at forty.
- Counting month-ends by feel. A birth date on the 29th, 30th or 31st needs a rule, not an instinct, and different people reach for different rules.
The most common of these by a wide margin is the first. It is also the one people are most confident about, which is why an age on a form is wrong more often than you would expect. If you want the full list with worked examples of each failure, we wrote it up in seven mistakes people make doing date maths by hand.
“How old am I” is usually small talk. Occasionally it is not, and in those cases the years-months-days form is the one that is asked for:
- Immigration and visa paperwork. Many application forms ask for age at the date of application in years and months, and a mismatch against the birth date on the passport gets flagged.
- Paediatric and medical records. Dosing, growth percentiles and developmental milestones are read in months for under-twos and in years and months after that.
- School and sport age groups. Eligibility is normally set by age on a fixed cut-off date, not age today, so you need to be able to work out an age at an arbitrary date rather than the current one.
- Pensions and benefit thresholds. These turn on the exact day you attain an age, which is why the leap-day question above is not academic.
- Insurance and lending. Premiums and terms often step at a birthday, so knowing you are 39 years and 11 months rather than “about 40” can be worth money.
If you need an age at a date other than today, a cut-off, a policy start, a hearing, use the date difference calculator with the birth date and that date, which reports the same years-months-days breakdown between any two points. To compare two people instead, the age difference calculator gives both current ages and the exact gap between them.