Baby Age Calculator

See your baby's exact age in months, weeks and days. Add the original due date if they were born early to get corrected age.

How baby age is calculated

Age is counted in whole calendar months plus the leftover days, which is how most pediatric charts and milestone lists describe it. Weeks and total days are shown too, since newborn guidance is usually in weeks.

What is corrected age?

Corrected (or adjusted) age subtracts the weeks a baby was born early. A baby born 8 weeks early who is 6 months old has a corrected age of about 4 months. Pediatricians often use it for milestones and growth until about age 2.

Using age for milestones and growth

Developmental checklists, growth charts and feeding guidance are all organized by age, so knowing the exact number helps you read them correctly. In the first months, advice is often given in weeks: "around 6 weeks" for a first social smile, for example. Later it moves to months, and by the toddler years to years and months.

Milestones are ranges, not deadlines. Most checklists describe what most babies can do by a certain age, and it is normal for a baby to be ahead in one area and behind in another. If something worries you, your pediatrician can look at the whole picture at a well-child visit.

Corrected age for babies born early

A baby born early has had less time to develop than a baby of the same age born on their due date. Using corrected age makes fair comparisons possible. For example, a baby born 10 weeks early who is 6 months old has a corrected age of about 3½ months, so their milestones are compared with those of a 3½-month-old.

Doctors usually use corrected age for development and growth for the first 2 years. By then most babies born early have caught up, and the difference stops mattering.

Frequently asked questions

At what age should I stop counting in weeks?

Many parents switch to months around 3 months, and by about 2 years most people use years and months.

Should I use corrected age for vaccines?

No. Vaccines are normally given by actual (chronological) age. Ask your pediatrician if you are unsure.

Why do months and days differ from weeks?

Calendar months are different lengths, so a month is not exactly 4 weeks. That is why both are shown.

How do I work out corrected age myself?

Take your baby's actual age and subtract the number of weeks they were born early. A 20-week-old baby born 6 weeks early has a corrected age of 14 weeks.

Is a baby born at 37 weeks premature?

No. Babies born at 37 weeks or later are term babies, so corrected age is not usually needed. Premature (preterm) means born before 37 weeks.