Tools · Baby
Baby Age Calculator: How Many Weeks or Months Old Is My Baby?
Free baby age calculator. Enter your baby's date of birth to see their exact age in completed months, total weeks, and total days.
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This article is for general information and is not a substitute for professional medical advice. Always consult your pediatrician or doctor about your child.
Sources: WHO, CDC, AAP and NHS guidance. Recommendations differ between countries — for local advice see the NHS or CDC.
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Add this only if your baby was born early, to see corrected age.
Enter your baby's date of birth to see their age.
How your baby's age is calculated
This calculator shows your baby's chronological age — the time since birth — in three ways: completed months plus leftover days, total whole weeks, and total days. Weeks are the unit most often used in the first few months ("my baby is 10 weeks old"), while months become more common later.
If your baby was born early, enter the original due date as well and the fourth card shows corrected age. For gestational age at birth, how many weeks early your baby arrived, and which age is used for growth charts versus vaccinations, see the corrected age calculator.
Everything is calculated on your device — nothing is stored or uploaded.
Frequently Asked Questions
How is my baby's age calculated?
Chronological age is counted from your baby's date of birth to today. This tool shows it as completed months plus remaining days, as total weeks, and as total days. Months are counted by the calendar (so the day-of-month is preserved), which is why a baby born on the 15th 'turns' a new month on the 15th.
How many weeks old is my baby in months?
As a rough guide, 4 weeks is about 1 month, 8 weeks about 2 months, and so on — but weeks and calendar months don't line up exactly (a month averages about 4.3 weeks). This calculator shows both at once so you don't have to convert. For medical purposes, weeks are usually preferred in the early months.
Should I give my baby's age in weeks or months at appointments?
In the first two to three months, weeks are the more precise unit and the one clinicians usually expect — "nine weeks" says more than "two months". From about four months, completed months become the normal way to describe age. If you are ever unsure, giving the date of birth removes the ambiguity entirely, and this calculator shows both units at once so you can use whichever the person asking prefers.
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