What this age calculator does
You enter a date of birth and a date to measure to. The date to measure to defaults to today, which is 2026-09-16. The calculator then counts your age in whole years first. It adds the leftover calendar months, then the leftover days. You see the result as years, months and days on one line.
The same page also gives you other views of the same span. You get your total months, total weeks and total days alive. You get the weekday you were born on. You get the number of days until your next birthday and the age you will turn on that day. If you want to check a date other than today, change the second date and every number updates.
How the months are counted
Months here are calendar months, not fixed blocks of 30 days. That means the day count inside a month changes with the month. A month can be 28, 29, 30 or 31 days. This is why two people born one month apart can have different day totals at the same age.
The rule for a partial month follows the calendar. January 31 plus one month is February 28 in a normal year, or February 29 in a leap year. January 31 to March 1 is 1 month and 1 day. The calculator applies the same rule to your birth date, so the answer matches how people normally talk about age.
Every day in the count is 24 hours. Daylight saving changes are not counted, so a day never has 23 or 25 hours here. This keeps the day totals stable no matter where you live or when the clocks change.
Worked example
Say you were born on 1990-05-20 and you want your age on 2026-09-16.
- Whole years: from 1990-05-20 to 2026-05-20 is 36 years.
- Remaining months: from 2026-05-20 to 2026-09-20 would be 4 months, but 2026-09-16 is 4 days short of that, so the month count is 3.
- Remaining days: from 2026-08-20 to 2026-09-16 is 27 days.
Your exact age is 36 years, 3 months and 27 days. The total months is 435. The total days is about 13,268. Your next birthday is 2027-05-20, which is 246 days away, and you will turn 37.
Birthdays on February 29
A February 29 birthday only exists in a leap year. Leap years happen every 4 years, except century years that are not divisible by 400. So 2024 and 2028 are leap years, and 2100 is not.
For the next-birthday countdown, a February 29 birthday falls on March 1 in a non-leap year. That keeps the countdown moving forward instead of skipping a year. Your age in years still increases on that date, the same as anyone else born in late February.
Other ways age is counted
Some countries count age differently from the year-month-day method used here. For example, Korean age was a traditional way of counting that did not match the Western system. This calculator uses the standard whole-years-then-months-then-days method. If you need a different local convention, treat the numbers here as one clear reference point and adjust from there.
Related date tools
If you need the gap between two dates without a birth date, the date calculator gives days, weeks and months between any two dates. For working days only, the business days calculator skips weekends and any holidays you list. To add or subtract time, use the time calculator.