Age Difference Calculator
Compare two dates of birth to find the exact age gap in calendar years, months and days. See each person’s age on a selected date, the total-day difference and upcoming birthdays.
How the age difference is calculated
The earlier birth date is treated as the starting date and the later birth date as the ending date. The calculator finds the greatest number of complete calendar months between them, separates those months into years and remaining months, and then counts the remaining days.
Age gap = completed calendar years + remaining completed months + remaining days.
Total days are calculated independently by subtracting the two UTC calendar-date serials. The decimal-year equivalent divides total days by 365.2425, the mean Gregorian year; it is a secondary conversion and does not replace the calendar result.
Checked examples
| Person A birth date | Person B birth date | Exact age difference |
|---|---|---|
| January 15, 1990 | March 20, 1995 | 5 years, 2 months, 5 days |
| March 20, 1995 | January 15, 1990 | 5 years, 2 months, 5 days |
| February 29, 2020 | February 28, 2021 | 1 year, 0 months, 0 days using month-end clamping |
| January 31, 2024 | February 29, 2024 | 0 years, 1 month, 0 days |
| December 31, 2025 | January 1, 2026 | 0 years, 0 months, 1 day |
| June 10, 2000 | June 10, 2000 | 0 years, 0 months, 0 days |
How to use the calculator
- Enter both dates of birth.
- Choose the date on which their individual ages should be shown.
- Select Calculate age difference.
- Review the fixed birth-date gap, individual ages, total days and next birthdays.
- Use Swap people to confirm that the magnitude of the gap does not depend on input order.
Limits and interpretation
- Dates from 1600 through 2400 are supported.
- The comparison date must be on or after both birth dates.
- Dates are evaluated without birth times or time zones, so the result does not include hours.
- A birthday on the 29th, 30th or 31st is clamped to the last valid day when the comparison month is shorter.
- The exact calendar gap and decimal-year conversion use different representations and should not be expected to display identical decimals.
- The tool reports arithmetic only. It does not judge compatibility, relationship suitability, legal capacity, school placement or eligibility.
Frequently asked questions
Does the age difference change over time?
The total-day difference between two birth dates is fixed. The displayed difference between completed whole-year ages can appear to change between birthdays, which is why this calculator reports the underlying calendar gap.
Who is older?
The person with the earlier date of birth is older. If the dates match, neither person is older by calendar date.
Are leap years included?
Yes. Total days include every February 29 between the dates, and calendar components use actual month lengths.
Can I compare siblings, partners or children?
Yes. The relationship label does not affect the arithmetic. The result should not be interpreted as advice about a relationship or eligibility rule.
Related calculators
Use the Age Calculator for one person’s exact age, the Birth Date Calculator by Age to reverse a known age, or the Date Calculator for general calendar intervals.