Baby Age Calculator
Enter your baby's date of birth to see their age in weeks and days, in months and days, and in total days. If your baby was born early, add the original due date to see the corrected age as well.
Free, no sign-up. What you enter stays in your browser: it is not saved or sent to HerFound. Reviewed .
Add this if your baby was born early, to see the corrected age.
Enter your baby's date of birth to see their age.
This is general information, not medical advice. It cannot take your own health history into account. For anything that worries you, speak to a doctor, midwife or pharmacist.
How it works
Total days = today's date minus the date of birth. Age in weeks = total days ÷ 7, with the remainder shown as days.
Age in months is counted on the calendar. A baby turns one month older on the same day of each month as the day they were born. If that day does not exist in a month, the last day of the month is used: a baby born on 31 January is one month old on 28 February (29 February in a leap year). The days left over are counted from that monthly date.
Corrected age (also called adjusted age) = actual age minus the time the baby was born early. Time born early = due date minus date of birth. This is the same as counting the age from the due date. The calculator shows it when a baby was born more than 3 weeks before the due date, which means before 37 weeks of pregnancy.
Corrected age is normally used until a child is 2 years old. It gives a fairer picture of when a premature baby may reach milestones such as smiling, sitting and walking.
What it cannot tell you
- It cannot tell you whether your baby is developing as expected. Babies reach milestones at different ages. If you are worried about your baby's development, feeding or growth, speak to your health visitor, paediatrician or doctor.
- Corrected age depends on the due date being right. Use the due date your clinic gave you, ideally the one from the dating scan.
- Vaccinations are usually given by actual age from birth, not corrected age. Ask your baby's doctor or nurse if you are not sure which age to use for something.
Apps that do this for you
A calculator answers once. These apps keep track over time. Compare all pregnancy and parenting apps.
Baby Connect
A baby tracker: log sleep, feeds and diapers and share it with every caregiver, on phone, web and Apple Watch.
Baby Daybook
A baby tracker: feeds, sleep, nappies and growth, with sleep predictions and family sync
BabyCenter
A pregnancy and baby tracker: week-by-week updates, handy tools, articles and a parent community.
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Common questions
To calculate a baby's age in weeks, count the days from the date of birth to today and divide by 7. The whole number is the weeks and the remainder is the extra days. For example, 45 days old is 6 weeks and 3 days.
Corrected age is a premature baby's actual age minus the number of weeks they were born early. A baby who is 20 weeks old and was born 8 weeks early has a corrected age of 12 weeks. It is the age the baby would be if they had been born on their due date.
Corrected age is normally used until a child is 2 years old. The American Academy of Pediatrics says that during the first 2 years it gives a better idea of when a baby born early should reach developmental milestones. After that, most children are assessed by their actual age.
A baby is not exactly one month old at 4 weeks, except in a 28-day February. Four weeks is 28 days, while a calendar month is 28 to 31 days. A baby born on 10 March is 4 weeks old on 7 April and one month old on 10 April.
A baby is premature (preterm) when born before 37 weeks of pregnancy, which is more than 3 weeks before the due date. This calculator shows a corrected age only for babies born that early. Babies born from 37 weeks are not usually given a corrected age.