Compare two people by birthdate, birth year, or current age. Birthdates provide a calendar gap and total days; the simpler modes show what can be established from less precise information.
Choose the information you know
Birthdates gives the most detailed result: years, months, days, total days between births, and each person's age today. Input order does not change the size of the gap. The result identifies the older person.
Birth years subtracts the two years without inventing birthdays. Ages subtracts the ages you enter. Decimal ages are accepted, but a decimal fraction of a year is not converted into calendar months because calendar months have different lengths.
Formula
birth-year gap = absolute value of (year 1 − year 2)
entered-age gap = absolute value of (age 1 − age 2)
date gap = complete calendar months plus remaining days
Examples
Two known birthdays
January 1, 1990 and June 15, 1993 are 3 years, 5 months, and 14 days apart. The person born in 1990 is older. The gap stays the same as both people age.
Only the years are known
Birth years 1990 and 1993 give a 3-year birth-year difference. Depending on the birthdays, the actual gap could be just over two years or almost four years. Enter complete dates to resolve it.
Comparing reported ages
Ages 30 and 25 differ by 5 years. If those ages are rounded down to whole birthdays, they do not establish an exact five-year difference between birthdates.
Calendar conventions and precision
The birthdate calculation starts at the earlier date, counts whole months, and then counts remaining days. Twelve complete months form a year. Month-end anniversaries are clamped to the last available day, so January 31 to February 28 is one calendar month in a non-leap year. Total days gives a separate measure that does not depend on month length.
Birthdates must be in year 1000 or later. This tool compares dates, without times of birth or timezone offsets. It rejects future birthdates when today's date is available. Current ages refresh with the page's current date; the birthdate gap itself does not change. Use the age calculator for age on a specific comparison date, or the date calculator for adding and subtracting calendar intervals.
Interpreting an age gap
An age difference describes a calendar interval. It does not measure maturity, compatibility, or legal eligibility. For school enrollment or other rules, use the required cutoff date and the institution's stated age convention.