How to use
Pick your “Date of birth” and the result appears. “Reference date” starts out as today’s date on the device you are using. If you need your age on another day, such as a school enrollment date or the day a contract is signed, change the reference date to that day. The “Today” button takes you back to today.
The result has four parts.
- Age: the largest number. Just below it, a line such as “You will turn 37 on Mon, March 15, 2027.” gives your next birthday and the age you turn that day.
- Exact age (years, months, days): the same age with the time since your most recent birthday spelled out in months and days.
- Next birthday: the days left, written like D-168. The number after D- is the number of days remaining, and the reference date itself is not counted. If the reference date is your birthday, you see “Today” (when the reference date is today) or “D-Day” (when it is any other day) instead of a number.
- Day of life: a day count that treats the day you were born as day 1.
How age is calculated
Take the year of the reference date, subtract the year you were born, then subtract 1 more if the reference date falls before your birthday that year. Your age goes up on the birthday itself. Someone born on September 21, 2000 is 25 on September 20, 2026 and turns 26 on September 21. Only the two dates go into the calculation, so the hour you were born makes no difference.
Worked examples
With the reference date set to September 28, 2026, the results are:
| Date of birth | Age | Exact age (years, months, days) | Next birthday | Day of life |
|---|---|---|---|---|
| March 15, 1990 | 36 | 36 years 6 months 13 days | D-168 | 13,347 |
| September 21, 2000 | 26 | 26 years 0 months 7 days | D-358 | 9,504 |
| December 10, 2000 | 25 | 25 years 9 months 18 days | D-73 | 9,424 |
The person born on December 10, 2000 has not had their birthday yet on the reference date, so 1 comes off the 26 you get from the years alone, leaving 25. The person born on September 21, 2000 is a week past their birthday, which is why the exact age reads “26 years 0 months 7 days”. On September 20, 2026, the day before that birthday, it read “25 years 11 months 30 days”, and on the birthday it rolled over to “26 years 0 months 0 days”.
How the months and days are counted
Months are counted from your most recent birthday. A month is complete each time the calendar reaches the same day number as your birthday. In a month that has no such day, it is complete on the last day of that month.
Here is how that plays out in 2026 for someone born on August 31, 1990.
| Reference date | Exact age (years, months, days) |
|---|---|
| September 29, 2026 | 36 years 0 months 29 days |
| September 30, 2026 | 36 years 1 month 0 days |
| October 30, 2026 | 36 years 1 month 30 days |
| October 31, 2026 | 36 years 2 months 0 days |
September has no 31st, so the first month was complete on the 30th. That does not shift every later month to the 30th. October has a 31st, and the second month is complete on the 31st again.
Why “Day of life” and the exact age differ by one day
“Day of life” counts the day you were born as day 1. If you were born on January 1, 2026, January 1 is day 1 and January 10 is day 10. On that same January 10, “Exact age (years, months, days)” reads “0 years 0 months 9 days”. It only counts the days that have gone by since the day of birth, so it comes out one lower. When you want to find your 100th or 1,000th day, read the “Day of life” value.
What this calculator doesn’t cover
- Time of birth: everything is worked out in whole dates. A late-night birth and an early-morning birth on the same date give the same result, and the calculator does not tell you an age in hours.
- Korea’s year age and counting age: only the ordinary age that goes up on your birthday is calculated here. The Korean Age Calculator shows those two Korean ages next to it.
- The age gap between two people: there is only one date of birth field. To see how many years and months lie between two birth dates, enter both in “Between two dates” in the Date Calculator.