Age calculator
Enter a birth date and any reference date to get the exact age in years, months and days, total days lived and the next birthday.
Calendar-date arithmetic; local dates are used, not timestamps.
How this calculator works
Exact age is not simply a year count: it is the difference measured from the birth date, borrowing a month at a time so that the days part stays correct. Someone born on 15 June 1990 is 36 years, 4 months and 7 days old on 22 October 2026 — and 13,278 days old in total, because leap years add a day roughly every four years.
Total days is the figure you need for medical forms, immigration paperwork and some benefit calculations. The next-birthday output handles the leap-day edge case: if you were born on 29 February, in non-leap years the birthday is treated as 1 March. Use the reference date field to answer “how old will I be on that date?” — retirement ages, application deadlines and age limits are all measured from a specific date, not from today.
The formula
Let the birth date be B and the reference date A. First compute years = A.year − B.year, then borrow months and days so that each part is non-negative:
days = A.day − B.day (if negative: borrow days in A's previous month)
months = A.month − B.month (if negative: borrow 12 months)
years = A.year − B.year (minus 1 if months were borrowed)
total days = (A − B) in daysThe total-days figure is an exact calendar difference, so it includes every leap day in between.
Worked example
For a birth date of Jun 15, 1990 measured on Oct 22, 2026, the exact age is 36 years, 4 months, 7 days. That is 13,278 days lived, and the next birthday falls on Jun 15, 2027.
Common mistakes
- Subtracting years only. A naive year difference can be a whole year off before the birthday has passed.
- Using 365 days per year for total days. Leap years add an extra day every four years, which adds up over a lifetime.
- Forgetting time zones. For age limits, the date that matters is the local date where the rule applies, not the date on your device.
Frequently asked questions
How is age calculated exactly?
Full years first, then whole months since the last birthday, then leftover days. The three parts together describe the elapsed time precisely; total days is the same period counted as days.
Why is my age in days different from 365 × years?
Because of leap days and because the months since your last birthday are not a whole fraction of a year. The exact calendar difference is the number that matters.
How do you handle a 29 February birthday?
In non-leap years the birthday is treated as 1 March for the purpose of the next-birthday date. Age in whole years still advances on the normal anniversary logic.
Related calculators
Date Difference CalculatorCountdown CalculatorBusiness Days CalculatorPregnancy Due Date Calculator · All Dates & Time calculators