How to use it
- Enter the date of birth.
- Enter the gestational age at birth: weeks and extra days, for example 32 and 3 for 32+3.
- The “age on” date is today; change it to see the corrected age on another day.
- Read the corrected age in months and days, and in weeks, plus the actual and postmenstrual ages.
How it works
Corrected age = chronological age − (40 weeks − gestational age at birth)
That is the same as counting age from the day the baby reached 40 weeks. The months and days are counted on the calendar from that day, the weeks from the day count. Postmenstrual age is gestational age at birth plus the days since birth. Before the 40-week date there is no corrected age yet, so the calculator shows the postmenstrual age instead.
Worked example
A baby born on 4 May 2026 at 32+0 weeks, seen on 3 November 2026:
- actual age 183 days = 26 weeks 1 day;
- born 8 weeks early, so 40 weeks was reached on 29 June 2026;
- corrected age 183 − 56 = 127 days = 18 weeks 1 day, or 4 months 5 days;
- postmenstrual age 224 + 183 days = 58 weeks 1 day.
Tips
- Compare milestones and growth with the corrected age, but give vaccines by the actual age.
- Babies born at 37 weeks or later are term, so the correction is small and usually not used.
- Ask your baby’s doctor or health visitor if you are unsure about development; the calculator only does the date arithmetic.