How accurate is the weeks figure?

It is exact — it is derived directly from the precise number of calendar days between the two dates, not an approximation.

Age, Date & Calendar

Age in Weeks Calculator

Enter a date of birth to see your age in total completed weeks, plus the days left over.

Your calculation is performed in your browser.

Enter a date of birth to see the age in completed weeks.

The calculator finds the exact number of calendar days between your date of birth and the calculation date, then divides that exact figure by seven.

Total weeks = floor(total days ÷ 7); remaining days = total days mod 7.

Someone exactly 100 days old is 14 completed weeks and 2 days old.

—Because the underlying day count is exact, the weeks-and-remainder breakdown is exact too.