Your child's age in weeks and months

Why weeks and months?

Babies change quickly, so check-ups, vaccination schedules and development milestones are usually given in weeks in the first months, then in months until about age two, then in years.

How to calculate

• Weeks: subtract the birth date from today to get days, then divide by 7. That gives whole weeks plus the remaining days.
• Months: count whole months from the birth day in each month; a baby born on the 10th turns a month older on the 10th of each month.

Example

Born Tuesday 10 March 2026, on 23 September 2026:

Enter the birth date in the Age Calculator to see all of this at once, plus the first birthday on both calendars.

Uneven months

A baby born on 31 December 2025 turns two months old on 28 February 2026, because February has no 31st and its last day is used. To find the date your child reaches a given age, say 6 or 9 months, add the months to the birth date with the Date Calculator.

Corrected age for premature babies

For babies born early, doctors sometimes use a “corrected age” (age minus the number of weeks the baby arrived early) when assessing development. This is a medical judgement; follow your doctor’s guidance.

This article covers calculating age only; for vaccination and check-up timing, follow the schedule of your health authority and your child’s doctor.

Last updated: 23 September 2026