How your age is worked out
The calculator counts whole years from your date of birth, then the leftover whole months, then the remaining days - the same way you would read a birthday off a calendar. Because months are different lengths, it counts real calendar months rather than dividing by an average, so a single month can be 28, 30, or 31 days depending on where it falls.
The same age is also shown as a single total in days, in weeks, and in whole months, so you can read it whichever way you need. All of the date math is done in UTC, so results are the same no matter where or when you open the page.
Next birthday and leap days
The calculator finds the next anniversary of your birth date, counts down the days to it, and shows the age you will turn. For a Feb 29 birthday it marks the day on Feb 29 in leap years and on Mar 1 in non-leap years.
Related calculators
Need to count between two arbitrary dates instead? Use the date duration calculator. Expecting a baby? The due date calculator estimates the arrival date from your last period.
Frequently asked questions
How is my exact age calculated?
The calculator counts whole years from your date of birth to today, then the leftover whole months, then the remaining days. Because months vary in length, it counts calendar months (clamping to each month's length) rather than dividing by an average, so the result lines up with how a birthday actually falls on the calendar.
How many days old am I?
The result card shows your total age in days, which is simply the number of days between your date of birth and the reference date. The same total is also shown in weeks and in whole months so you can read your age whichever way you need.
What day of the week was I born?
The calculator works out the weekday of your date of birth and shows it as 'Born on a ...'. The date math is done in UTC so the weekday is stable no matter where you open the page from.
When is my next birthday?
The calculator finds the next anniversary of your birth date that falls strictly after the reference date, shows that date, counts down the days to it, and tells you the age you will turn on that day.
Does it handle leap years and Feb 29?
Yes. Day counts already span leap days correctly. For a Feb 29 birthday, the calculator celebrates on Feb 29 in leap years and falls back to Mar 1 in non-leap years, which is the common convention for marking a leap-day birthday.