The Age in Weeks and Days calculator expresses any age or date span as whole weeks plus the leftover days. This is the format used for infant age, pregnancy and milestone tracking, and any situation where months are too coarse or vary too much in length. Enter a date of birth (or any start date) and an end date to get the breakdown instantly.
How it works
The tool counts the exact number of whole days between the start and end dates, then divides that total by 7. The integer part of the division is the number of complete weeks, and the remainder is the leftover days (0 to 6). It also shows the raw total weeks (as a decimal) and the total days, so you have every form of the answer at once. The end date defaults to today but can be set to any later date.
Example
A baby born on 1 January 2026, measured on 12 March 2026:
The span is 70 days. 70 ÷ 7 = 10 with a remainder of 0, so the baby is 10 weeks and 0 days old — exactly 10 weeks.
| Output | Value |
|---|---|
| Weeks | 10 |
| Days | 0 |
| Total days | 70 |
All the arithmetic happens in your browser, so your dates never leave your device.