Baby Age Calculator

Enter your baby’s birth date to see their exact age in months and days, in weeks, and in total days. If your baby was born early, add the original due date and we’ll also show the corrected age that many milestones are measured against.

Baby’s birth dateOriginal due date (optional)Add this only if your baby was born early, for corrected age.

General information only, not medical advice. For any concern about your baby’s growth or development, including how to use corrected age, talk to your healthcare provider.

How it works

Babies are often described in weeks for the first couple of months and in months after that, which can get confusing fast. This calculator gives you all the common ways at once — calendar months and days, total weeks, and total days — straight from the birth date.

For babies born preterm, “corrected age” adjusts for how early they arrived: it’s the age counted from the original due date rather than the birth date. Health professionals use it to set fair expectations for growth and milestones, usually up to about age two.

Frequently asked questions

What is corrected age? +

Corrected (or adjusted) age is your baby’s age calculated from their original due date instead of their birth date. For a baby born 6 weeks early, you subtract those 6 weeks — so at 4 months old, their corrected age is about 2.5 months.

When should I use corrected age? +

It’s most useful for babies born more than a couple of weeks early, when judging development and growth. Professionals typically use corrected age until around 24 months, after which the gap matters less.

How is age in months counted? +

We count whole calendar months from the birth date, then the extra days — so “3 months, 12 days” means three full calendar months plus 12 days, which lines up with how checkups are usually described.

Why does the week count differ from months? +

Weeks are exact (7-day blocks of total days lived), while calendar months vary in length. Both are correct — they’re just two different ways of measuring the same age.