Age Calculator
Find completed years, additional months and days on a chosen date, with an explicit month-end convention.
Last updated: November 4, 2026
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Quick summary: Find completed years, additional months and days on a chosen date, with an explicit month-end convention.
Read the complete guide
Updated reference sections in this guide are in English.
Age on a date you choose
Enter a birth date and the date you want to compare it with. The second field initially uses today according to your device, but you can change it to check a past or future anniversary. The result shows completed years, additional completed months and the days since that monthly anniversary. Total calendar days is also displayed.
How years, months and days are separated
First, the calculator finds the greatest whole number of calendar months from the birth date that does not pass the comparison date. It divides those months into completed years and additional months, then counts the days from that monthly anniversary to the comparison date. Months are counted from the original birth date, rather than repeatedly adding a shorter month to an already shortened date.
Additional months = completed calendar months modulo 12
Remaining days = comparison date − last completed monthly anniversary
The month-end convention
When an anniversary day does not exist in a target month, this tool uses the last day of that month. January 31 plus one calendar month therefore lands on February 28 in a common year, or February 29 in a leap year. Under the same convention, a February 29 birthday reaches its annual anniversary on February 28 in a common year. This is a stated calculation convention, not a ruling about legal age.
Examples you can check
A birthday has just passed
For a birth date of June 15, 2000 and a comparison date of November 2, 2026, the result is 26 years, 4 months and 18 days. The monthly anniversary used for the remaining-day calculation is October 15, 2026.
A leap-day anniversary
For February 29, 2000 to February 28, 2025, the result is 25 years, 0 months and 0 days under the shorter-month convention stated above.
A date before the birthday
For June 15, 2000 to June 14, 2026, the completed year count is still 25. The additional months and days describe progress toward the next birthday, not a rounded-up age.
Check this scenario in the calculator:
- Date of birth
- 2000-02-29
- Age on this date
- 2026-10-31
Where an age estimate needs another rule
This form does not decide eligibility for benefits, school admission, a contract or an age-restricted service. Those uses may have a jurisdiction-specific cutoff, a different leap-day rule, or a requirement based on exact time of birth. The tool uses dates without times and the Gregorian calendar throughout. A comparison date before the birth date is rejected.
Age questions
Why is total days not simply years multiplied by 365?
Calendar years include leap days, and the additional months have different lengths. Total days is counted directly from the two dates.
Can I check age on a future date?
Yes. Change the comparison date. It must be on or after the birth date.
Does the form need a name or identity number?
No. Only the two dates are used, and the calculator does not submit those dates to a calculation service.