What the calculator returns
Two numbers come from one birth date: your current age, broken into years, months and days, and the whole days left until your next birthday. Both are measured against today, or against any target date you enter.
How the two figures are counted
- Years, months, days. Full years first, then the extra months and days since your last birthday. When the day count goes negative, it borrows days from the previous month, so month lengths of 28 to 31 days are handled.
- Days to next birthday. Your birthday for the current year if it is still ahead, otherwise the same date next year. The gap in whole days is the countdown; a birthday today reads zero.
- Leap years. They shift the exact day count, and a 29 February birthday needs the 28 Feb / 1 March rule in non-leap years.
Why an age result can differ by a year or two
The number above is chronological age, the international standard: you are zero at birth and gain a year on each birthday. A few traditional systems count differently, which is why some tools disagree.
| System | How it counts |
|---|---|
| International (chronological) | Zero at birth, plus one each birthday |
| Traditional Korean (pre-2023) | One at birth, everyone adds a year on 1 January |
| Traditional Chinese | One at birth, plus one each Lunar New Year |
South Korea moved to the international system in June 2023. This calculator uses the international count.
Common questions
How is exact age worked out in years, months and days?
Subtract the birth year from the current year, then adjust: if your birthday has not happened yet this year, drop a year. The leftover months and days are counted forward from your last birthday, borrowing days from the previous month when needed.
How are the days until my next birthday counted?
The next birthday is your birth month and day in the current year, or next year if it has already passed. The result is the number of whole days from today to that date. If your birthday is today, the count is zero.
What happens if I was born on 29 February?
In non-leap years the legal birthday falls on 28 February in the US and on 1 March in the UK and many other countries. Your age still counts as the full number of years since birth, so nothing about the year total changes.
