A baby age calculator in weeks, months and days
In the first months everyone asks how old your baby is — and the answer changes with who is asking. Doctors and baby apps count in weeks, family counts in months, and some celebrations count days. This baby age calculator gives all three from the date of birth: weeks and days, months and days, and the total number of days, for today or any date you choose.
It also shows which week and month of life your baby is in, when they turn the next whole week and month, and a table of key age points — 6 weeks, 3 months, 100 days, 6 months, the first birthday and more — with how many days are left. Everything is worked out in your browser; nothing is stored or sent.
How to use the Baby Age Calculator
- Enter your baby’s date of birth.
- Leave Age on as today, or pick another date — an appointment, a trip or a photo date. Press Today to jump back.
- Read the age in weeks and days, months and days, and days old; the lines below say which week and month of life it is and when the next week and month are reached.
- Check the key age dates table for upcoming points, then press Copy result to paste the age into a message or a baby book.
Baby Age Calculator features
Weeks, months and days
Age in completed weeks plus days, calendar months plus days, and total days, side by side. After two years it switches to years and months.
Week and month of life
A baby who is 10 weeks and 5 days old is in week 11 — the way many baby books and apps number weeks.
Next week and month
The date your baby turns the next whole week (same weekday as the birth) and the next whole month.
Key age dates
1 and 2 weeks, 6, 10 and 14 weeks, 1 to 4 months, 100 days, 6 and 9 months, 1 year, 15 and 18 months and 2 years, with days to go.
Any date
Work out how old your baby was on a past date or will be on a future one.
How the age is counted
Weeks are exact: the number of days since birth divided by seven, with the remainder as days. A baby born on Monday 10 August 2026 is 10 weeks and 5 days old on Saturday 24 October 2026, which is 75 days.
Months are calendar months, as people say them: from 10 August to 10 October is 2 months, and from there to 24 October is 14 more days. Months are 28 to 31 days long, so weeks and months do not convert exactly — one month is about 4.35 weeks. A baby born on the 31st completes a month on the last day of a shorter month (28 February, 30 April), and a 29 February baby has a birthday on 28 February in common years, the same rules as the age calculator.
Week of life counts the first seven days as week 1, so a baby who is 10 weeks and 5 days old is in week 11. Some apps instead say “10 weeks” for the whole of that week; both describe the same age.
Weeks or months: which to use?
Health workers usually talk in weeks for about the first three months, because a lot changes week to week and check-ups are set in weeks — India’s national immunization schedule, for example, has visits at 6, 10 and 14 weeks, then at 9–12 months and 16–24 months (Ministry of Health and Family Welfare). After that, months are more natural, and after two years, years and months. Feeding, sleep and milestone guides are usually grouped by month — see the baby milestones checklist, the baby sleep schedule and the baby feeding chart.
Premature babies and pregnancy weeks
- Born before 37 weeks: this page gives the chronological age, counted from birth. For growth charts and milestones, doctors use corrected (adjusted) age — the chronological age minus the number of weeks the baby was born early — usually until age 2. The corrected age calculator does that, including postmenstrual age.
- Still pregnant? “Baby age by LMP” means the pregnancy week counted from the first day of the last menstrual period. Use the pregnancy due date calculator for gestational age and the due date.
- Vaccines: the vaccination schedule lists the doses by age; your clinic’s card is the one to follow.
Baby Age Calculator FAQ
How do I calculate my baby’s age in weeks?
Count the days from the date of birth to today and divide by seven: the whole number is the weeks and the remainder is the days. Enter the birth date above and it is done for you, along with months and days.
How many weeks old is a 3-month-old baby?
About 13 weeks. Three calendar months are 89 to 92 days depending on the months, so a baby turns 3 months old at 12 weeks and 5 days to 13 weeks and 1 day.
When is my baby 6 weeks old?
Exactly 42 days after birth, on the same weekday as the birth. The key age dates table shows the date.
Is my baby 2 months old at 8 weeks?
Not quite always. Eight weeks is 56 days, while two calendar months are 59 to 62 days, so most babies turn 2 months a few days after 8 weeks.
Should I use corrected age for my premature baby?
For growth and development checks, usually yes until about age 2 — ask your paediatrician. This page shows chronological age; the corrected age calculator gives the adjusted age.