How to Calculate the Age Difference Between Two People
The age difference — or age gap — between two people is simply the span between their two dates of birth. Unlike each person's age, which climbs every day, the gap between them is fixed the moment the younger one is born and never changes again.
The simplest method
Take the two dates of birth and find the span between them. If one person was born on 3 March 1990 and the other on 20 September 1994, the difference is the time from the first date to the second. The Age Difference Calculator does this directly — enter both birth dates and it returns the gap.
Expressing the gap in years, months, and days
A precise age difference is given the same way an age is: complete years, then remaining months, then leftover days, using real month lengths and accounting for leap years. Rounding to whole years ("four years apart") is fine in conversation, but the exact figure matters for records and eligibility rules. The method behind it is covered in how age is calculated.
Why the gap never changes
Both people get older at the same rate, so the distance between their ages stays constant. Two siblings born four years and two months apart are always four years and two months apart, whether they are toddlers or pensioners. This is what makes an age difference different from an age: an age needs "as of today", but a gap does not.
Related calculations
To find a single person's age instead of a gap, use the Age Calculator. And if you just want the raw number of days between the two birth dates — handy for comparisons — the Days Between Dates calculator gives the plain count.