Adjusted Age Calculator

From a baby's date of birth and original due date, this calculator works out the chronological age, how early the baby was born and the corrected age, and lists when the corrected age reaches 1 to 24 months.

How to use

1. Enter the "Date of birth".
2. Under "What you know", choose "The due date" and enter the "Original due date", or choose "Weeks of pregnancy at birth" and enter the weeks and "Extra days".
3. "As of" is today. Change it to see another date; "Set to today" brings it back.
4. "When the corrected age is reached" lists the dates for corrected ages of 1 to 24 months, with the chronological age on each date.

How it works

• Corrected age = chronological age − time born early, the same as the age counted from the due date. Time born early = due date − date of birth.
• Exact days are used. Some programmes round the weeks down or the months to whole numbers.
• For reference only, not medical advice. How long and how the corrected age is used is decided by your baby's care team.
• Your entries are saved only in this browser for your next visit.

Questions and answers

How do you calculate corrected age?

Subtract the time born early from the chronological age. A baby born at 30 weeks who is now 20 weeks old was born 10 weeks early, so the corrected age is 10 weeks.

Can I use the weeks of pregnancy instead of the due date?

Yes. The due date is worked back as date of birth + (40 weeks − gestational age). Born at 33 weeks 4 days, the due date is 45 days after birth.

What if the due date has not come yet?

Corrected age starts on the due date, so before it the page shows "Before the due date" and the days left until then.

Until what age should corrected age be used?

It differs between programmes and checks, so the tool does not set an age. Follow your care team's guidance.