Subtracting birth year from this year only gives a rough age. To say someone is 31 years, 2 months and 27 days old, you have to deal with months of different lengths. This article shows the hand method step by step, with worked examples, and then explains what the Age Calculator app does with the same problem.

Why simple subtraction is not enough

If someone was born in 1995 and it is 2026, the quick answer is 31. That is only correct if their birthday has already passed this year. Before the birthday they are still 30. And if you want months and days, you need more than the year.

Exact age means counting complete years first, then complete months after the last birthday, then the days left over. It sounds fiddly, but it is the same idea as telling the time: you count whole units first and leave the remainder to the smaller unit.

The hand method, step by step

Write the birth date and today's date as day, month, year.

Subtract the years.…