Baby Age Calculator (Weeks & Months)
The Baby Age Calculator tells you exactly how old your baby is in weeks and in months. Enter your baby's date of birth and today's date, and it returns the age in weeks (plus extra days), the number of completed calendar months, and the total days lived. It's handy for tracking milestones, vaccination schedules, and age-based clothing or feeding guides.
Formula
Weeks = total days ÷ 7 (with remainder days); Months = completed calendar months since birth
- The calculator counts the days between the birth date and today, then expresses that span in weeks and in calendar months.
- Weeks = whole weeks in the total days, with any leftover shown as extra days; total days = today − date of birth.
- Months counts completed calendar months, so a baby born on the 15th becomes 'one month' on the 15th of the next month.
- Input definitions: • Baby's date of birth: the day your baby was born. • Today's date: the date you want the age calculated for (defaults to a sample date).
- Pediatricians often use weeks for the first few months and months thereafter, which is why both are shown.
- Age in weeks is useful for vaccination timing and developmental milestones during the newborn period.
Example Calculation
Inputs
- Baby's date of birth: 2026-01-01
- Today's date: 2026-06-01
A baby born on 1 January 2026, viewed on 1 June 2026, has lived 151 days. That's 21 weeks and 4 days, or 5 completed calendar months.
Frequently asked questions
How is my baby's age in weeks calculated?
The calculator counts the total days since birth and divides by 7. The whole number is the weeks, and the remainder is the extra days.
How are months counted?
By completed calendar months. A baby born on the 10th turns one month old on the 10th of the next month, regardless of how many days that month has.
Why show both weeks and months?
Doctors usually describe newborns in weeks and older babies in months. Vaccination and milestone charts use both, so the tool shows each.
Does this account for leap years?
Yes. It counts the actual number of days between the two dates, so February 29 and varying month lengths are handled automatically.
What is corrected age?
For babies born prematurely, corrected age subtracts the weeks of prematurity. This tool shows actual (chronological) age — use a corrected-age calculator for preemies.
Can I use it for any date?
Yes. Set 'today's date' to any date to find your baby's age on a birthday, doctor visit, or other milestone.
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