Age Difference Calculator
The exact age gap between two people from their birth dates — years, months and days, total days and weeks, and who is older.
The gap is counted the way ages are: completed calendar years from the earlier birthday, then completed months, then days.
How the age difference calculator works
The gap is counted the way ages are: completed calendar years from the earlier birthday, then completed months, then days. It does not depend on today’s date, and it is the same whichever person you enter first. The total-days row uses the actual calendar, leap days included.
Formula: gap = completed years, months, days between the two birth dates
Worked examples
| Inputs | Age difference | Note |
|---|---|---|
| 2 March 1985 and 15 June 1990 | 5 years, 3 months, 13 days | 5 years, 3 months, 13 days |
| Twins born a day apart | 1 day | 1 day |
| A year and a leap day | 1 year, 1 day | 1 year, 1 day |
FAQFrequently asked questions
Does today’s date matter?
No — the gap between two birth dates is fixed. Both people age at the same rate, so the difference never changes.
How are months counted?
As completed calendar months from the earlier birthday, the way ages are counted: 2 March to 15 June is 3 months and 13 days whatever the lengths of the months between.
What about leap days?
Total days use the real calendar, leap days included. A 29 February birthday is treated as 28 February in the year-month-day breakdown for non-leap years.
Why do the whole-months and total-days rows not divide neatly?
Because months are 28 to 31 days long, the same number of months can span a different number of days depending on where in the year the gap falls.
Where these figures come from
- ISO 8601 — Date and time — Representations for information interchange — the yyyy-mm-dd format and the week-numbering rules used here
- US Naval Observatory — Calendars — the Gregorian leap-year rule
- US Office of Personnel Management — federal holidays — federal holidays (not applied here)
Last checked: September 2026. The Gregorian calendar rules do not change; working-day counts exclude Saturdays and Sundays only.