Baby Age Calculator
See a baby's age in weeks, months and days, including corrected age for babies born early.
About the Baby Age Calculator
Enter the date of birth to see exactly how old a baby is today, or on any other date, in months, weeks and days. Health visitors, baby books and feeding guides switch between these units, so having all three in one place saves the arithmetic.
For a baby born before 37 weeks, enter the weeks of pregnancy at birth to also see the corrected (adjusted) age: actual age minus the weeks born early. Paediatricians use corrected age for growth charts and developmental milestones until about 2 years old; vaccinations follow actual age.
The formula
Corrected age = age − (40 − gestational weeks at birth)
- age
- days since birth
- 40
- weeks of a full-term pregnancy
- gestational weeks at birth
- how many weeks pregnant the mother was at delivery
How to read your result
- Whole months are counted from the birth date: a baby born on the 15th turns 1 month old on the 15th of the next month.
Worked example
Born 15 March 2026 at 32 weeks; age on 11 November 2026
- Actual age: 241 days = 34 weeks 3 days, 7 months
- Born 40 − 32 = 8 weeks (56 days) early
- Corrected age: 185 days = 26 weeks 3 days, about 6.1 months
Things to keep in mind
- Corrected age is a guide for milestones; every baby develops at their own pace. Ask your health visitor or paediatrician about any concerns.
Questions people ask
When do I stop correcting?
Usually around 2 years, when most preemies have caught up.
Do vaccines use corrected age?
No, they follow chronological (actual) age.
How many weeks is 6 months?
About 26 weeks. Months vary from 28 to 31 days, so the exact count depends on the dates.