How it counts
weeks old = days since birth ÷ 7days counted exactly on the calendar
- date of birth
- the starting date
- count to
- the date to measure at
- weeks old
- whole days lived, divided by seven
For the first few months, weeks are the usual way to give a baby's age; after that, months and years are more common.
Frequently asked questions
How many weeks old is my baby?
Enter the birth date and leave the second date as today; the tool shows the age in weeks.
How many weeks is a 3-month-old?
About 13 weeks, though it varies by a few days with the month lengths.
Why give a baby's age in weeks?
Growth and development in early infancy are tracked week by week, so weeks are more precise than months.
Does it count exact days?
Yes, and the weeks are those days divided by seven.