Age Difference Calculator

How to use

1. 1Enter both people's dates of birth. The name fields are optional and only used in the summary copy.
2. 2Pick the date you want to compare ages on. Keep Use today checked for a live answer, or uncheck it and pick any past or future date.
3. 3Read the headline result: who is older and by exactly how many years, months, and days, with total days, weeks, and months between the two birthdays.
4. 4Open the Ages on this date panel to see each person's full age on the target date, including totals in days, weeks, and months.
5. 5Use the Side-by-side moments panel to read the older person's age when the younger was born, the date the younger person reaches the older's current age, and the days between the two births.
6. 6Click Swap A and B to switch the order, Reset to today to re-anchor the target date, or Copy summary to copy a short paragraph of the result.

About this tool

Age Difference Calculator compares two dates of birth and answers the questions people actually search for: how much older one person is than another, what their ages are on a chosen date (today by default), and when the younger person reaches the older person's current age. The math is calendar-aware, not just a raw day count: the gap is reported in years, months, and days, with the months and days correctly borrowed when the younger person's birth day-of-month is earlier than the older person's, so February-born and December-born siblings report the answer you would write on paper. The Ages on this date panel runs each person's birthday through a target date you pick (or live today), and shows their full age in years, months, and days alongside total days, weeks, and calendar months lived. A side-by-side moments panel surfaces the three points everyone wants to know: the older person's age when the younger one was born, the date the younger person will reach the older person's current age (computed by adding the older person's exact calendar age back onto the younger person's birth date), and the count of days the younger person was still unborn when the older was born. A relative age stat reports the younger person's share of the older person's life as a percentage, which is the right number to cite when comparing childhood milestones, lap times, or career timelines. Names are optional and live in the summary copy so the result reads naturally; a Swap A and B button reverses the order, a Reset to today button re-anchors the target date, and a Copy summary button packs the result into a short paragraph you can paste into a message. Everything runs locally; the dates you enter, the names you type, and the target date you pick are never uploaded to a server.

Free to use. Works in your browser. No signup, no login.