Baby Age Calculator

Parents and pediatricians measure a baby’s age in a few different ways, and they do not always line up. For the first couple of months, age is usually counted in weeks, because so much changes week to week and the common screenings and vaccine schedules are timed that way. After that, months become the normal unit, though a baby who is 8 weeks old is not quite the same as one who is 2 calendar months old, since months have different lengths.

This calculator gives you all of them at once: completed weeks plus the leftover days, completed calendar months, and the total number of days your baby has been alive. It counts full weeks and months the way a doctor would, ignoring the partial week or month in progress rather than rounding up.

There is a second age that matters for babies born early, called corrected or adjusted age. It is the age the baby would be if they had arrived on the original due date, and you find it by subtracting the weeks of prematurity from the actual age. A baby born two months early who is four months old has a corrected age of about two months, and that corrected figure is the fairer yardstick for milestones like rolling over, sitting, and first words through the first two years. Enter the due date and you will see both. Every baby develops on their own clock, so treat any milestone range as a guide rather than a deadline, and bring real concerns to your pediatrician.