Age Calculator
Calculate exact calendar age in years, months and days for any selected date. The results also show total days lived, completed weeks, birth weekday and the next birthday.
How age is calculated
The calculator first finds the greatest number of complete calendar months from the birth date to the selected age date. Those months are then separated into complete years and remaining months. Any calendar days after that monthly anniversary become the day component.
Exact age = complete years + remaining complete months + remaining calendar days. Total days are calculated independently by subtracting the birth-date serial from the selected-date serial.
For birthdays on the 29th, 30th or 31st, a month without that day uses its final valid date. A February 29 birthday therefore uses February 28 in a non-leap year for this calculator’s calendar arithmetic. Legal conventions can differ.
Checked examples
| Date of birth | Age date | Result |
|---|---|---|
| January 15, 2000 | September 16, 2026 | 26 years, 8 months, 1 day |
| September 16, 2026 | September 16, 2026 | 0 years, 0 months, 0 days |
| February 29, 2024 | February 28, 2025 | 1 year, 0 months, 0 days using month-end clamping |
| February 29, 2024 | March 1, 2025 | 1 year, 0 months, 1 day |
| January 31, 2024 | February 29, 2024 | 0 years, 1 month, 0 days |
| December 20, 1990 | September 16, 2026 | 95 days until the next birthday |
How to use the Age Calculator
- Enter the complete date of birth.
- Keep today’s date or choose another date for a historical or future age.
- Select Calculate age.
- Review exact age, total days, completed weeks, birth weekday and next birthday.
Limits and interpretation
- Dates from 1600 through 2400 are supported.
- The selected age date cannot precede the date of birth.
- Total days are calendar days. “Completed weeks” is a conversion of those days, not a count of work or school weeks.
- The result does not include hours, minutes or seconds because no birth time or time zone is entered.
- Rules for leap-day birthdays can differ for legal eligibility, insurance, contracts and government programs. Confirm the applicable rule rather than relying only on this calculator.
Frequently asked questions
Can I calculate age on a past date?
Yes. Enter the past date in “Age on this date,” provided it is not earlier than the date of birth.
Does the result account for leap years?
Yes. Total days and calendar components include February 29 whenever it occurs.
Why are years and months not fixed numbers of days?
Calendar years contain 365 or 366 days, and calendar months contain 28 to 31 days. The calculator uses actual calendar boundaries instead of fixed averages.
Is a February 29 birthday treated as February 28?
For this calculator’s month-end arithmetic, yes in a non-leap year. A legal or contractual rule may instead use March 1.
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