Age Difference Calculator

This calculator answers two questions at once: which of two people was born first, and how much time — years, months, days — separates their births. Each date is read in the calendar you choose for it; the span appears on both calendars and as a day count, followed by each person's current age.

The method

The gap between two ages equals the distance separating the birth days themselves, so it holds steady however much time passes. Starting from the earlier birth, the tool counts whole years, then whole months, then the remaining days. Any Hijri date is first matched to its Gregorian day using the Umm al-Qura table.

A worked case

Two births: 8 October 1985 (23 Muharram 1406) and 21 January 1988 (1 Jumada al-Thani 1408):

1. Born first: the person from October 1985
2. Span on the Gregorian calendar: 2 years, 3 months, 13 days
3. Span on the Hijri calendar: 2 years, 4 months, 8 days
4. Day count: 835, identical on both calendars

Two calendars, one span

The number of days between the births never changes; what changes is the unit used to count them. A lunar year runs roughly eleven days short of a solar one, so the same span reads slightly longer when measured in Hijri years.

When a birthday is missing from the calendar

Someone born on 29 February completes each year on 1 March in non-leap years. The same goes for the 30th of a lunar month that runs to only 29 days in some years: the year completes at the start of the following month. Ages and spans both follow this rule.

Typical uses

• Telling which of two relatives born the same week is the elder.
• Seeing how much older a parent is than each child, in years and months.
• Comparing a Hijri-recorded birth date with a Gregorian one without converting by hand.
• Getting the span between two births as an exact day count.

For spans between any two dates, business days included, open the date span calculator. For your own current age in Hijri and Gregorian, plus the wait until your birthday, try the age calculator for both calendars. To match one date across Hijri and Gregorian, use the Hijri date converter.