Age Calculator
Calculate an exact calendar age from a date of birth and an age-at date. See completed years, months, and remaining days alongside total days, weeks, completed months, and approximate hours lived.
Age Calculator tool
About the Age Calculator
Use today's date for a current age or choose a past or future date for a milestone. The calculator also shows the weekday of birth and the countdown to the next birthday relative to your selected date.
How Is Age Calculated?
Age is calculated with calendar anniversaries rather than dividing days by 365. Completed years are counted first, with invalid anniversaries clamped to the last day of the month. Up to 11 completed months are then counted from that anniversary, followed by remaining days.
Total days = (target UTC midnight − birth UTC midnight) ÷ 86,400,000
Total months = 12 × completed years + completed months after the yearly anniversary
Hours = total days × 24
Example
From January 1, 2000, to March 2, 2024, the age is 24 years, 2 months, and 1 day. The interval contains 8,827 days, or 1,261 weeks.
How to Use the Age Calculator
- Enter the date of birth.
- Choose the date on which age should be measured.
- Read the years, months, and days in the main result.
- Compare completed months with total weeks and days lived.
- Check the birthday countdown and the stated leap-day convention.
Age Calculator Examples
A birthday on the target date
From June 15, 1990, to June 15, 2025, the age is exactly 35 years, 0 months, and 0 days. The birthday countdown is zero.
A short-month boundary
From January 31, 2023, to March 1, 2023, the age is 0 years, 1 month, and 1 day: the monthly anniversary is clamped to February 28.
A leap-day birthday
From February 29, 2020, to February 28, 2021, the age is 1 year, 0 months, and 0 days under the February 28 anniversary convention.
Calendar borrowing
A monthly anniversary that would fall outside a month is moved to that month's final day. This avoids negative remaining-day results around February and other short months.
Years are counted first and months are limited to 0 through 11. With leap-day births, the remainder can reach 31 days near the next leap-year birthday because the prior yearly anniversary was clamped.
Date-only limitations
All dates use the Gregorian calendar and UTC midnight. No time of day or birthplace is required.
This is a calendar calculation, not a legal determination of age eligibility. Verify the relevant jurisdiction's rules for official use.
Frequently Asked Questions
How are February 29 birthdays handled?
The anniversary is February 28 in a non-leap year and February 29 in a leap year. Legal and cultural birthday conventions may differ.
Why not divide days by 365?
Years and months have different lengths. Calendar anniversaries preserve the relationship between the birth date and the selected date.
Can I calculate age on a future date?
Yes. Choose any valid age-at date on or after the date of birth, within years 0001 through 9999.
Are hours lived exact?
No. Hours are total calendar days multiplied by 24. The calculation does not include time of birth, local daylight-saving transitions, or leap seconds.
Does total months include a partial month?
No. It is 12 times completed years plus the completed months in the displayed calendar-age breakdown. Weeks are shown as a rounded decimal.