Age Calculator
Enter your date of birth to find your exact age, how many days until your next birthday, and more.
Last updated: August 2026 · Written and verified by Akash Pandey
Calculate your age
Age (years)
This runs the same calculation engine as the main scientific calculator, entirely in your browser. Nothing you type is sent anywhere.
How is age actually calculated?
The naive method - current year minus birth year - is wrong for roughly a third of the year: it gives an age that is one year too high for anyone whose birthday has not yet occurred this calendar year. The correct method compares three components in order: year, then month, then day. Subtract birth year from current year; if the current month/day falls before the birth month/day, subtract 1 more.
Why the leap-year rule is more subtle than "every 4 years"
A calendar year averages 365.25 days because Earth's orbit takes about 365.2422 days, not a whole number - so a purely 365-day calendar would drift by about a day every four years. The Gregorian calendar's actual rule is: a year is a leap year if divisible by 4, except century years, unless they are also divisible by 400. That is why 2000 was a leap year but 1900 and 2100 are not - "divisible by 4" alone would get both of those centuries wrong.
is_leap = (year % 4 == 0) AND (year % 100 != 0 OR year % 400 == 0)
- A person born on 29 February exists on the calendar only in leap years - by convention, their birthday is usually observed on 28 February or 1 March in other years.
Age in different units
| Unit | Formula | Example (25 years) |
|---|---|---|
| Years | direct | 25 |
| Months | years × 12 + months | 304 |
| Weeks | days ÷ 7 | 1,304 |
| Days | years × 365.2425 | 9,131 |
| Hours | days × 24 | 219,150 |
| Minutes | hours × 60 | 13,149,000 |
Worked example
Born 20 November 1995, checked on 3 March 2026 - how old?
2026 − 1995, adjusted for month/day
- Given: birth date 20 Nov 1995; today 3 Mar 2026.
- Method: subtract years first, then check whether the birthday has occurred yet this year.
- Calculation:
2026 − 1995 = 31. Today (3 Mar) falls before the birth month/day (20 Nov), so subtract 1 more:31 − 1 = 30. - Interpretation: the person is 30, not 31 - the naive year-only subtraction would have overstated their age by a full year.
= 30 years old
Frequently Asked Questions
Why does "current year minus birth year" sometimes give the wrong age?
It ignores whether the birthday has already happened this year. Someone born in November, checked in March, has not had their birthday yet this year - the correct age is one less than the simple year subtraction gives. The fix is to compare month and day, not just year.
Why is 2000 a leap year but 1900 was not?
The Gregorian rule adds a century exception: years divisible by 100 are not leap years, unless also divisible by 400. 1900 ÷ 400 is not a whole number, so it was a common year; 2000 ÷ 400 = 5 exactly, so it was a leap year. Without this refinement, the calendar would drift from the solar year by about 3 days every 400 years.
How do I calculate age in months rather than years?
Multiply the whole years by 12, then add the extra months since the last birthday. Someone who is "25 years and 4 months" old is 25 × 12 + 4 = 304 months old.
What happens to someone born on 29 February in a non-leap year?
Their birth date does not exist on the calendar that year. Most institutions treat 28 February or 1 March as the observed birthday, but this is a convention rather than a mathematical rule - different countries and systems choose differently.
Why does the "365.25 days per year" figure use .2425 in the day-count formula above?
365.25 is the simple average implied by "one leap day every 4 years". The Gregorian calendar's century exception refines this to 365.2425 days per year on average, which is closer to Earth's actual orbital period (365.2422 days) - the extra precision matters over centuries, not over one lifetime.
How do I calculate someone else's age, not just my own?
Use their date of birth instead of yours - the year/month/day comparison method above works identically regardless of whose birth date it is.
Why does my age differ on different websites?
Some sites count full years only, while others may round up or use a different calendar system. This calculator uses the standard year-month-day comparison, which is the most common method.
How do I calculate age in days?
Multiply the total years by 365, add the leap days (one for each leap year between the two dates), then add the extra days since the last birthday. The calculator above does this automatically.