How is age calculated between two dates?

It counts full years first, then full months, then the remaining days. From 15 March 2000 to 10 March 2024 that is 23 years, 11 months and 26 days — the last year is not complete yet, so it is not counted. This is why age is not simply the day count divided by 365.

Does the calculation handle leap years?

Yes. Every fourth year contributes a 29 February, and the calculator counts calendar days rather than assuming 365. A person born on 29 February ages one calendar year at a time like everyone else; only the birthday itself falls on a leap year, which is why 28 February or 1 March is the usual celebration in common years.

Why does my age in months not match my age in years times twelve?

Because months are unequal and the count only runs to complete months. Twenty-three years and eleven months is not the same as 287 months, since the leftover days are not yet a month. Use the three-part answer — years, months, days — rather than trying to convert everything into a single unit.

Is someone legally an age on the birthday or the day after?

On the birthday. Age increases at the start of the anniversary date, so a person is 18 from the moment their eighteenth birthday begins. Some systems — driving licences, school intake, insurance brackets — use a cut-off date such as 1 September instead, which is a policy choice rather than a date calculation.

Why do doctors say my child is 34 months instead of 2 years 10 months?

Months are the unit that changes fast enough to be useful. Between birth and about three years, growth, dosing and development are tracked month by month; after that, years become adequate. Both come from the same calendar arithmetic this calculator performs — the difference is only which pair of numbers gets written down.

Calculate Your Exact Age in Years, Months and Days

Most people know their age in years. But how old are you in months? In days? In hours? If you were born on February 29, do you celebrate your birthday every year or only on leap years? An age calculator answers these questions instantly.

What I Tested

I used the Age Calculator with three different dates of birth.

• DOB: January 15, 1990. As of September 13, 2026: 36 years, 7 months, 28 days. Total days lived: 13,373. Next birthday in 4 months, 2 days. All values matched manual verification accounting for leap years.

• DOB: February 29, 2000 (leap year baby). As of September 13, 2026: 26 years, 6 months, 15 days. Total days lived: 9,693. The calculator correctly handled the leap year birthday.

• DOB: December 31, 2025. As of September 13, 2026: 0 years, 8 months, 13 days. Total days lived: 256. Demonstrates the calculator works for very young ages too.

How It Works

The calculator counts the complete years between your date of birth and today, then counts the remaining complete months, then the remaining days. It accounts for varying month lengths (28-31 days) and leap years (February 29 in divisible-by-4 years, except century years not divisible by 400).

When You Need This

A parent tracking their baby's exact age in months for pediatrician visits. Someone born on February 29 checking if this year they get a real birthday. An HR manager verifying age for retirement eligibility. A government office requiring exact age in days for legal purposes. Anyone curious about how many days they have been alive. Exact age in months also decides which BMI percentile band a child falls into, which is why the BMI percentile chart for kids asks for age down to the month.

Step-by-Step

(1) Open the Age Calculator. (2) Enter your date of birth using the date picker. (3) See your exact age in years, months, and days instantly. (4) Check total days lived and next birthday countdown below the main result.

How It Compares

Timeanddate.com has an age calculator but loads external resources and shows ads. Calculator.net works but has a cluttered interface. Our tool runs instantly in your browser with no account, and also shows total days lived — a feature most free age calculators skip.

Limitations

The calculator uses calendar dates only — it does not account for time of birth. Future dates are not supported. Age is calculated from date of birth to today's date only. Counting the days between two arbitrary dates instead of from a birth date? Use the Date Difference Calculator.

Privacy

Your date of birth is processed entirely in your browser. It is never sent to any server. No one at FreeDigitalToolkit can see the date you enter.

Why Exact Age Is Not Just Days Divided by 365

Dividing the day count by 365 drifts immediately. A year containing 29 February has 366 days, months run between 28 and 31, and after a decade the error is visible. The calculator therefore walks the calendar: subtract the birth date from the reference date field by field, borrowing from the month column when the day is smaller and carrying a year when the month column goes negative.

That is also why the answer has three parts. Years answer how many birthdays have passed, months answer how long since the last one, and days are what remains. Reporting only the years hides eleven months of difference between two people who are both, technically, forty.

Where Exact Ages Actually Matter

Legal thresholds are date-precise: licence eligibility, voting, drinking age, retirement rules and insurance brackets all switch at midnight on an anniversary, not when a rounded number changes. Genealogy and record-keeping need the same precision, because a birth record written as an age in years cannot be reconciled with a later document without the months and days.

The same applies in reverse — employment records, pension contributions and school placement all depend on the reference date, not today. If you are checking an age for a document, use the date that document cares about rather than the current date, and keep the three-part answer in the file.

Age in Months for Medical and School Contexts

Pediatricians dose by weight, not age, but appointment notes and growth charts still record age in years and months — a child of 2 years 11 months is tracked differently from one of 3 years 0 months at the same weight. Schools use the same cutoff logic for entry years, where a difference of days changes the placement.