Age Calculator
Find exact age in completed years, months and days, total days and days to the next birthday, with clear 29 February and month-end rules.
Dates
Completed years, months and days between two calendar dates.
Enter a date of birth and press Calculate.
How the count works
- Whole months step from the birth day of the month. If that day does not exist, it clamps to the month’s last day — 31 January + 1 month = 28 February (29 in a leap year).
- Remaining days are counted from that last whole month to the as-at date.
- Total days is a date-only difference: no times of day, time zones or daylight saving are involved.
- This is chronological calendar age. Legal age rules (for example, the moment a birthday takes effect) vary by jurisdiction and are not decided here.
How to use this calculator
- Enter the date of birth.
- Leave “Age as at” blank for today (your device's date in its own time zone) or pick any later date.
- For a 29 February birth date, choose whether common-year birthdays fall on 28 February or 1 March, then press Calculate.
How it works
Completed years and months are counted from the birth date's day of the month. When that day does not exist in a month it clamps to the month's last day, so 31 January + 1 month = 28 February (29 in a leap year). Remaining days are counted from the last whole month to the as-at date.
Total days is a date-only difference with no clock times, time zones or daylight saving involved. A birth date after the as-at date is rejected.
This is chronological calendar age, not a legal age determination — rules for when a birthday takes legal effect differ between jurisdictions.
Worked example
Born 2000-01-15, as at 2026-06-21. 26 whole years reach 2026-01-15 and 5 more months reach 2026-06-15, leaving 6 days: 26 years, 5 months, 6 days — 9,654 days in total. The next birthday is 2027-01-15.
Tips
- Runs entirely in your browser. Your inputs are not saved or transmitted.
Frequently asked questions
How are leap birthdays handled?
For someone born on 29 February you choose the common-year anniversary: 28 February (the same end-of-month clamp used for months) or 1 March. On 28 February 2001 someone born on 29 February 2000 is 1 year old under the first rule and 0 years, 11 months, 30 days under the second.
Which timezone is today?
If you leave the as-at date blank, “today” is your device's calendar date in its own time zone at the moment you press Calculate, and the result names that zone. Pick an explicit date to calculate for anywhere else.
Is this legal age?
No. It is calendar arithmetic. Laws can treat birthdays, leap days or times of birth differently, so check the rule that applies to you for any legal purpose.
Do my dates upload anywhere?
Runs entirely in your browser. Your inputs are not saved or transmitted.
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Cite this tool
Zerdly. (2026). Age Calculator. Retrieved from https://www.zerdly.com/tools/age-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.