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Date & Timeage

Age Difference Calculator

The gap between two birth dates in years, months and days. It borrows the way people do when counting, rather than dividing days by 365.

Also called: age gap calculator, difference between birthdays.

Age difference
4 years, 6 months and 7 days

4 years, 6 months and 7 days, or 1,652 days. The older was 4 years and 6 months old when the younger was born.

Days apart
1,652
Whole years
4
Additional months
6
Additional days
7
Age of the older at the birth
4 years and 6 months old
How this is calculated
Method and background

How this is calculated

Subtract the components and borrow when one goes negative: days borrow the length of the preceding month, months borrow twelve. That produces the answer people expect, unlike dividing total days by 365.25, which drifts and gives a fractional year nobody uses in conversation.

the same borrowing an age calculation uses, so the answer matches how people count
d1, d2
The two dates

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

four and a half years apart

First date of birth
1990-05-15
Second date of birth
1994-11-22

Age difference4 years, 6 months and 7 days

Counted by borrowing, verified by hand

Open this example

the same day is no difference

First date of birth
1990-05-15
Second date of birth
1990-05-15

Age difference0 years, 0 months and 0 days

boundary

Open this example

Method and limits

What it assumes

  • UTC dates, ignoring time of day.

What it deliberately does not model

  • Borrowing uses the length of the preceding calendar month, which is the usual convention.

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

Why not just divide the days by 365?
Because months are not equal and years are not 365 days. Borrowing matches how anyone would count it aloud, which is the point of the answer.