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Age Calculator

Find your exact age in years, months and days from a date of birth, plus total days and weeks lived and your next birthday.

What this tool does

Find your exact age in years, months and days from a date of birth, plus total days and weeks lived and your next birthday. You fill in these fields: Date of birth and As of this date. It shows age; years, months and days; total months; total weeks; total days; days until the next birthday; next birthday; and born on a.

Inputs

  • Date of birth: A date.
  • As of this date: A date. Starts as today's date. Starts as today. Change it to ask on any other date on or after the date of birth.

How to use

  1. Pick a date for "Date of birth".
  2. Pick a date for "As of this date".
  3. Read the result: age; years, months and days; total months; total weeks; total days; days until the next birthday; next birthday; and born on a. It appears once every required field has a valid value.

Worked examples

Example 1. Inputs:

  • Date of birth: May 15, 1990
  • As of this date: October 8, 2026

Results:

  • Age: 36 years
  • Years, months and days: 36 years, 4 months and 23 days
  • Total months: 436 months
  • Total weeks: 1,899 weeks
  • Total days: 13,295 days
  • Days until the next birthday: 219 days
  • Next birthday: May 15, 2027
  • Born on a: Tuesday

How this is worked out: Calendar count. 1990-05-15 + 36 years = 2026-05-15; + 4 months = 2026-09-15; Sep 15 to Oct 8 = 15 + 8 = 23 days. Total days: 36 * 365 + 9 leap days (1992, 96, 2000, 04, 08, 12, 16, 20, 24) = 13149 to 2026-05-15, then 31 + 30 + 31 + 31 = 123 to Sep 15 and 23 more = 13295. Weeks = floor(13295 / 7) = 1899. Next birthday 2027-05-15: 31 + 30 + 31 + 31 + 28 + 31 + 30 = 212 to May 8, + 7 = 219. 2026-10-08 is a Thursday; 13295 mod 7 = 2, so the birth date was a Tuesday.

Example 2. Inputs:

  • Date of birth: January 31, 2026
  • As of this date: March 1, 2026

Results:

  • Age: 0 years
  • Years, months and days: 0 years, 1 month and 1 day
  • Total months: 1 month
  • Total weeks: 4 weeks
  • Total days: 29 days
  • Days until the next birthday: 336 days
  • Next birthday: January 31, 2027
  • Born on a: Saturday

How this is worked out: End of month rule: Jan 31 + 1 month is Feb 28 (2026 is not a leap year), + 2 months would be Mar 31, past the date, so 1 month. Feb 28 to Mar 1 is 1 day. Total days = 28 + 1 = 29.

Example 3. Inputs:

  • Date of birth: February 29, 2000
  • As of this date: March 1, 2023

Results:

  • Age: 23 years
  • Years, months and days: 23 years, 0 months and 1 day
  • Total months: 276 months
  • Total weeks: 1,200 weeks
  • Total days: 8,401 days
  • Days until the next birthday: 365 days
  • Next birthday: February 29, 2024
  • Born on a: Tuesday

How this is worked out: A person born on Feb 29 completes a year on Feb 28 in a common year, so 2000-02-29 + 23 years = 2023-02-28, then 1 day to Mar 1. Total days: 2000-03-01 to 2023-03-01 is 23 * 365 + 5 leap days (2004, 08, 12, 16, 20) = 8400, plus 1 day from Feb 29 to Mar 1 2000 = 8401. The next Feb 29 on or after 2023-03-01 is 2024-02-29.

Example 4. Inputs:

  • Date of birth: October 8, 2026
  • As of this date: October 8, 2026

Results:

  • Age: 0 years
  • Years, months and days: 0 years, 0 months and 0 days
  • Total months: 0 months
  • Total weeks: 0 weeks
  • Total days: 0 days
  • Days until the next birthday: 0 days
  • Next birthday: October 8, 2026
  • Born on a: Thursday
  • Note: It is a birthday on that date.

How this is worked out: Born today: no time has passed, so every count is 0, and the birthday falls on today. Born on the date measured: the birthday is today, so 0 days remain. 2026-10-08 is a Thursday (2026-01-01 is a Thursday and Oct 8 is day 281, and 280 is a multiple of 7).

Where this comes from

Age from a date of birth. Completed years are counted first, then completed months, then the days left over, all from the date of birth. A person born on February 29 completes a year on February 28 in a year that is not a leap year. The next birthday is the next time the day of birth comes round, on or after the date measured. Source: The Gregorian calendar: month lengths, the leap year rule (every fourth year, except century years not divisible by 400) and the seven-day week.

Limitations

  • Works with calendar dates only. It does not use the time of birth or a time zone.
  • Uses the Gregorian calendar for every date, including dates before it was adopted.
  • The date of birth must be on or before the date being measured.
  • Zodiac signs are not shown.

FAQs

Q: How is the age worked out?
A: It counts completed years first, then completed months, then the days left over, all measured from the date of birth.
Q: What happens if the date of birth is February 29?
A: In a year that is not a leap year, the year is counted as complete on February 28, and the next birthday is shown on February 28.
Q: Can I ask on a date other than today?
A: Yes. Change the second date to any day on or after the date of birth.
Q: What if the birthday is on the date measured?
A: The next birthday is that day and the count of days until it is 0.
Q: How is the day of the week found?
A: It is worked out from the calendar date itself, using the Gregorian calendar, so it does not depend on a time zone.
Q: Why are minutes lived not shown?
A: Only calendar dates are used, not clock times or time zones, so an exact count of minutes cannot be given.

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