Age Difference Calculator
Free, with no sign up. Calculations run on your device; your entries stay in this browser.
Enter two birth dates, not ages. Dates use the proleptic Gregorian calendar for years 0001–9999. Order does not matter: the result is the nonnegative gap from the earlier date to the later date. Find the maximum whole months from the earlier date, clamping its original day to the destination month’s last day; split those months into years and months, then count remaining days. No current clock, time zones or relationship/eligibility judgments are used.
Your result
M = maximum whole months for which shift(earlier, M) ≤ later; years = floor(M/12); months = M mod 12; days = later − shift(earlier, M). Shift clamps the original day to the last day of the target month. Total days = (later midnight − earlier midnight)/86,400 seconds.
Primary source: RFC 3339, Gregorian dates and leap-year rules. The month-end decomposition is this tool’s declared convention.
Worked example
2023-01-31 to 2023-02-28 is 0 years, 1 month, 0 days under clamping, and 28 total days. 2000-02-29 to 2001-02-28 is 1 year, 0 months, 0 days and 365 total days.
How to use this tool
Enter the two birth dates and Calculate. Read both the calendar gap and total day count.
Frequently asked questions
What happens with a leap-day birthday?
The original day is clamped to the last day of the destination month. February 29 to February 28 in the next non-leap year counts as one calendar year.
Why can calendar months differ from a day count?
Gregorian months have different lengths. The calendar result uses the declared clamping convention; total days is the exact midnight-to-midnight difference.
Is this free and private?
Yes. These calculations run in your browser, without sign-up or uploading your entries.