Whole months
M = largest integer such that birth + M months ≤ reference date
Age calculator
Get an exact age in years, months and days, the total days and weeks lived and the date of the next birthday, as of today or any other date.
The date of birth must be valid and cannot be later than the reference date.
Exact age
Age expressed in
full months
full weeks
days
Next birthday
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How does this tool work?
This age calculator gives a person’s exact age in years, months and days from their date of birth. It uses today’s date by default, but you can pick any reference date: age on 31 December for a sports category, age on the day of an exam or a school cut-off date, or age when a contract starts. It also converts the age into months, weeks and days and shows the date of, and countdown to, the next birthday.
The calculation follows the calendar rather than an average. The tool first finds the last “monthly anniversary” reached: the date of birth moved forward by a whole number of months without passing the reference date. That number of months gives the years (in groups of 12) and the remaining months; the days are then counted from that last monthly anniversary to the reference date.
When the birth day does not exist in the target month, the anniversary is placed on the last day of that month: 31 January becomes 28 (or 29) February, 31 March becomes 30 April. This is the same rule as the “Add or subtract time from a date” tool and the JavaScript Temporal standard. Someone born on 29 February is therefore one year older on 28 February in common years.
The total in days is the exact difference between the two dates, leap days included (Gregorian rule: a year divisible by 4 is a leap year, except century years not divisible by 400). Weeks and months are complete units, rounded down. Dates are handled as calendar days without time or time zone, so daylight saving changes have no effect.
How to use this tool
Enter the date of birth
Type the day, month and year; the result appears as soon as the date is complete.
Choose the “age on” date
Keep today’s date or replace it with the date on which the age must be assessed.
Read and share the result
Check the exact age, the totals and the next birthday, then copy the calculation link if needed.
How exact age is computed
Age is broken down from the number of whole months elapsed since birth, then the remaining days.
Years and months
years = ⌊M ÷ 12⌋; months = M − 12 × years
Remaining days
days = reference date − (birth + M months)
Full weeks
weeks = ⌊total days ÷ 7⌋
- M
- number of complete months elapsed since birth
- ⌊x⌋
- integer part of x (rounded down)
A month has no fixed length, which is why age in years, months and days cannot be obtained by dividing a number of days by 30 or 365.25.
Use cases
Age on a cut-off date
Check age on 1 January or 31 December for a sports category, a competition or an administrative age limit.
A child’s exact age
Express age in months and days for a health record, a nursery application or school entry.
Age on a past date
Find an ancestor’s age at their wedding, an author’s age when a book came out, or anyone’s age at a historical event.
Counting days lived
Spot your 10,000th day or a round number of weeks in advance to celebrate it.
Examples
Age on 11 October 2026
The last monthly anniversary is 14 September 2026; from 14 September to 11 October there are 27 days left.
Input
Born: 14 May 1990
Reference: 11 October 2026Result
36 years, 4 months, 27 days
436 full months · 1,899 weeks · 13,299 days
Next birthday: 14 May 2027 (turning 37), in 215 daysBorn on 29 February
2027 is not a leap year, so the birthday falls on the last day of February.
Input
Born: 29 February 2004
Reference: 11 October 2026Result
22 years, 7 months, 12 days
Next birthday: 28 February 2027 (turning 23)Tips and best practices
- For a regulatory age limit (sport, exam, insurance), check in the rules which date the age is assessed on and enter it as the reference date.
- Age in months is the most useful measure for children under two; age in days is mainly for spotting round numbers (10,000 days ≈ 27 years and 4 months).
- To find out which day of the week you were born on, use the day of the week calculator.
- The calculation link keeps both dates in the address: handy to save or send a calculation, but do not share it if the date of birth is private.
Sources and references
- Claus Tøndering, The Gregorian Calendar (opens in a new tab), Calendar FAQPage in English
- ISO — ISO 8601 date and time format (opens in a new tab)Page in English
- TC39, Temporal.PlainDate (opens in a new tab), Temporal documentationPage in English
Frequently asked questions
How do I calculate my exact age?
Count the full years since birth, then the full months since the last birthday, then the days since the last monthly anniversary. The calculator does these three steps automatically, using the real length of each month.
How old is someone born on 29 February in a common year?
The tool treats them as one year older on 28 February, the last day of the month. Laws differ: some countries use 28 February, others 1 March. If a specific rule applies to you, move the reference date by one day to check.
Why is 31 January to 1 March “1 month and 1 day”?
31 January plus one month lands on 28 February (29 in a leap year), as there is no 31 February. From 28 February to 1 March there is 1 day left. Some calculators show “1 month and −2 days” or “29 days”; the last-day-of-month rule avoids such inconsistent results.
Are leap years taken into account?
Yes. Every 29 February crossed is included in the total days, following the Gregorian calendar rule. Between 14 May 1990 and 14 May 2026, for example, there are 13,149 days, including 9 leap days.
Can I calculate an age on a past or future date?
Yes. Replace today’s date with any date after the birth: age at a historical event, at a planned retirement or when a contract ends.
How does this differ from the date difference calculator?
The arithmetic is the same, but the age calculator adds the next birthday and rejects a reference date before birth. To measure any period, in either direction and with an “include the end date” option, use the date difference calculator.
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