How to calculate age
Age is a calendar number: it is computed between a birth date and a given date in years, months and days. This guide explains how the calculator works, how it handles leap years and 29 February birthdays, and gives a worked example matching Klar’s age calculator.
Age is a calendar calculation, not a time one
Age here means the calendar difference between the birth date and the calculation date: complete years, months and days. Time of day (hours and minutes) is not counted — the math runs on dates, not timestamps. The calculation handles varying month lengths and leap years automatically, because it is calendar-based rather than a fixed day count.
A worked example
Using the calculator’s values: born 2000-01-01, as of 2024-01-01. The result: age 24 years, that is 288 months, or 8,766 days, or 1,252 weeks. Days until next birthday: 0.
Leap years and 29 February birthdays
In non-leap years, someone born on 29 February is counted as turning a year older on 28 February or 1 March per the calendar. The calculator follows the calendar rather than the actual day count, so the age stays precise on a calendar basis.
Common mistakes
Among the mistakes: mixing Hijri and Gregorian dates (the calculator is Gregorian only), entering the calculation date as the birth date (yields age zero), and assuming age is measured in hours and minutes rather than dates.
Key takeaways
- Age = the calendar difference in years, months and days between birth and the calculation date.
- The calculation date is inclusive: it includes the day of the age itself.
- The calculation is Gregorian only, and time of day is not counted.
- 29 February birthdays count on 28 February or 1 March in non-leap years.
Frequently asked questions
How does the calculator handle 29 February births?
In non-leap years the birthday counts on 28 February or 1 March per the calendar, and age is handled on a calendar basis rather than actual days.
Is the calculator Hijri or Gregorian?
Gregorian only. To compute a Hijri age, first convert the Hijri date to Gregorian.