How this age calculator works
Your age is counted in whole calendar units. First it counts the full years since your birth date, then the full months since your last birthday, then the days left over. If you were born on 15 May 1990, on 23 September 2026 you are 36 years, 4 months and 8 days old: 36 birthdays have passed, the last one was on 15 May, four more monthly anniversaries have followed it (June to September), and 8 days have gone by since 15 September.
Months have different lengths, so when a birth date falls on the 29th, 30th or 31st, a shorter month counts its last day as the anniversary. Someone born on 31 January reaches one month old on 28 February, or 29 February in a leap year.
The totals (months, weeks, days and hours) count every calendar day between the two dates, including leap days. Hours are counted from midnight to midnight, so they are a whole-day figure rather than time of birth.
Birthdays on 29 February
If you were born on a leap day, you only get a true birthday every four years. In other years this calculator moves your birthday to 28 February, which is the most common everyday convention. Some countries use 1 March for legal purposes such as driving or voting age, so check the local rule when it matters.
Common questions
How accurate is this age calculator?
The result is accurate to the day, based on the calendar dates you enter. It doesn't need a time of birth, since age is conventionally measured in whole days, months and years rather than hours.
What if I only know the birth year, not the exact date?
Enter 1 January of that year to get a rough figure, and treat the result as an estimate rather than an exact age. The true age could be up to 364 days different, since the calculator has no way to know the real month and day.
Can I compare the ages of two different people?
Run the calculator twice, once for each date of birth, using the same Age on date both times. The two results can then be compared directly, or subtracted from each other to find the age gap between them.
Why does my age look one day off compared with another site?
Some calculators treat every month as 30 days or apply your local time zone, which can shift results near a month's end. This one uses real calendar months and works entirely in whole days, so a birthday always lands on the correct date.
Can I check my age on a future date, like a retirement or exam day?
Yes. Change the Age on date field to any date, past or future, and the age shown updates to match. This works just as well for a date years from now as it does for today.
Is my date of birth stored or sent anywhere?
No. The calculation runs entirely in your browser and nothing is sent to a server. If you share the page link after calculating, the dates are in the link itself, so only share it with people you're happy to see them.
Does it matter what time zone someone was born in?
No. Age is calculated from the calendar date alone, not the time of day, so the result is the same regardless of which time zone the birth took place in.