Baby Age Calculator
Baby's age in months, weeks and days, corrected age for preemies, and milestones.
About this tool
Enter your baby's date of birth and, if they were born early, the original due date. The calculator shows their age in calendar months and days, in weeks and in days, the corrected age counted from the due date, and the next few dates worth celebrating, such as the next month-birthday, 100 days, the half birthday and the first birthday. You can change the "age on" date to check any day.
How baby age and corrected age are counted
Baby age is usually counted in weeks for the first few months and then in months. A baby born on 1 March 2026 is, on 12 October 2026, 7 months and 11 days old, which is 32 weeks and 1 day or 225 days. If that baby was due on 5 April, they were born 35 days, or 5 weeks, early. Their corrected age, counted from the due date, is 6 months and 7 days. Health professionals use corrected age for growth charts and developmental checks until about two years, because a baby born early is developmentally closer to babies born on their due date. Month counting handles short months: a baby born on 31 January turns one month old on 28 February, or 29 February in a leap year. Honest limits: babies develop at their own pace, and milestone ages are broad ranges. Talk to your health visitor, midwife or doctor about any worries. Not medical advice. The due date calculator works out the due date, the age calculator handles older children and adults and the sleep calculator helps plan bedtimes for the grown-ups. Leap years, explained properly explains the 29 February case.
Frequently asked questions
How do I calculate my baby's age in weeks?
Count the days since birth and divide by 7. A baby born 225 days ago is 32 weeks and 1 day old.
What is corrected age?
Age counted from the due date instead of the birth date. A baby born 5 weeks early who is 7 months old has a corrected age of about 6 months.
Until what age is corrected age used?
Usually until about two years, after which most children born early have caught up.
Is my data saved?
No. The dates are used only on this page in your browser and nothing is stored or sent.