Enter your baby's date of birth to see their age in weeks, months and days. If they were born before 37 weeks, add the original due date to see their corrected age too.
Results are estimates for planning. Check the figures before you make a financial or health decision.
How the Baby age calculator works
The calculator counts the whole days from the date of birth to the date you choose (today by default), then shows that as weeks and days, as calendar months and days, and as a plain day count. It also gives the date of the next monthly birthday.
Corrected (adjusted) age is for babies born early. If you say your baby was born before 37 weeks and give the original due date, it works out how many weeks early they arrived and then counts age from the due date instead of the birth date. Before the due date is reached it tells you how many days are left.
- Months are calendar months, so a baby born on the 31st has a monthly birthday on the last day of shorter months.
- The tool covers babies and toddlers up to 3 years, and early births of up to 18 weeks before the due date.
- The general stage note is a broad guide only. For vaccinations and checks it simply points you to the NHS schedule and your baby’s Red Book.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Date of birth | 2026-07-27 |
| Age on | 2026-10-05 |
| Born before 37 weeks? | No, or not sure |
Age on 5 Oct 2026: 10 weeks, 0 days
| Age in weeks and days | 10 weeks, 0 days |
|---|---|
| Age in months | 2 months, 8 days |
| Age in days | 70 |
| Next monthly birthday | Tue, 27 October 2026 |
| General stage | Young baby. Routine checks at about 6 to 8 weeks are part of NHS care. |
| Vaccinations and checks | Check the NHS vaccination schedule and your baby’s Red Book |
Tips and common mistakes
Use corrected age when thinking about early development, but use the actual birth date for vaccinations and for the NHS schedule. Check the schedule and your baby’s Red Book rather than relying on any online tool. Babies vary a lot, so a stage that does not match your baby is rarely a worry on its own: raise any concerns with your health visitor or GP. Change the “Age on” date to plan ahead, for example to see how old your baby will be on a holiday. This is general information, not medical advice.
Frequently asked questions
What is corrected age?
Corrected age is a baby’s age counted from their due date rather than their birth date. It is used for babies born early, because they have had less time to develop than their birth date suggests.
When is a baby classed as premature?
In the UK a baby born before 37 weeks of pregnancy is considered premature. Your neonatal team or health visitor will explain how corrected age applies to your baby.
Does this tell me when vaccinations are due?
No. Vaccination dates are set by the NHS schedule, so check the current schedule and your baby’s Red Book or ask your GP surgery or health visitor.