Age Difference Calculator

How to find the age difference

Enter each person's date of birth — the order doesn't matter. The calculator works out who is older and shows the gap between the two birthdays in years, months and days.

Example: one person born 10 May 1990 and another born 22 November 1993 are 3 years, 6 months and 12 days apart.

The age gap never changes

Because both people get older at the same rate, the difference between their ages is constant over their whole lives — it is fixed the moment the younger one is born. So you can calculate it once from the two birth dates and it stays the same.

Common uses

• The age gap between partners in a relationship.
• The gap between siblings or twins (sometimes just minutes).
• Comparing classmates against a school year cutoff.
• Working out the gap between two historical figures or events.

Why subtracting the birth years gives the wrong answer

The quickest mental shortcut — subtract one birth year from the other — is right only by accident. Two people born in 1990 and 1993 might be anywhere from just over two years apart to almost four, depending on where their birthdays fall in the year.

The table shows how far off the year-subtraction shortcut can be for the same pair of years.

How the months and days are worked out

A gap in "years, months and days" has to deal with months of unequal length, so the calculation counts whole years first, then whole months, then the leftover days — the same way you'd count age itself.

That ordering is what makes the result stable: the days left over are always counted against the length of the month they fall in, rather than against an averaged 30-day month. Leap days are handled the same way, so a 29 February birthday is measured against 28 February in common years.

One consequence surprises people: the same gap can display as "1 year, 0 months, 30 days" in one direction and a slightly different day count if you count from the other end. That is a property of calendar months, not an error — the total number of days between the two dates never changes.

Age gaps in practice

• Siblings — a gap under about two years usually means overlapping school years; over four and they rarely share a school.
• School admission — many systems compare a child's age against a fixed cutoff date rather than against classmates, so calculate age on the cutoff date itself.
• Twins and multiples — the gap is minutes, but paperwork often needs it stated in days as zero.
• Relationships — the common "half your age plus seven" rule of thumb is a social convention, not a legal or medical standard.
• Legal questions — anything involving consent, guardianship or benefits depends entirely on local law and the specific dates; use the exact gap as an input, not as an answer.

Calculating it by hand

If you want to check the result, work from the younger person's birth date and count up: how many whole years until you pass the older person's birth date without overshooting, then whole months, then days. Counting up avoids the borrowing mistakes that make subtraction error-prone.

Example: from 22 November 1993 back to 10 May 1990 — three whole years reaches 22 November 1990, six more months reaches 22 May 1990, and 12 days back reaches 10 May 1990. That is 3 years, 6 months and 12 days.