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Baby Age Calculator
How old is your baby today? Enter the date of birth to get their exact age in days, weeks and months, when they turn the next month, and the dates of fun milestones like 100 days, the half birthday and 1,000 days.
Last updated:
Today by default
Enter your values to see the result.
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How to use the Baby Age Calculator
- Enter your baby's date of birth.
- Keep "Age on" as today, or pick another date such as a doctor's appointment.
- Add a name if you like, for a personal summary.
- Read the age in days, weeks and months and the next month milestone.
- Scroll to the milestone table for 100 days, the half birthday and more.
How baby age is calculated
- Days old = today's date − date of birth.
- Weeks old = days ÷ 7 (the remainder is extra days).
- Months old = whole calendar months since the birth date, plus the days since the last monthly birthday.
Example: born January 31, age on April 15 → 74 days = 10 weeks 4 days = 2 months (the 2-month mark falls on March 31) and 15 days.
Baby age conversion chart
| Months | Weeks (approx.) | Days (approx.) |
|---|---|---|
| 1 month | 4.3 weeks | 30 days |
| 2 months | 8.7 weeks | 61 days |
| 3 months | 13 weeks | 91 days |
| 4 months | 17.4 weeks | 122 days |
| 6 months | 26 weeks | 183 days |
| 9 months | 39 weeks | 274 days |
| 12 months | 52 weeks | 365 days |
| 18 months | 78 weeks | 548 days |
| 24 months | 104 weeks | 730 days |
Pediatric checkups and vaccine schedules are often set by age in weeks for newborns and by months afterwards, so it helps to know both.
Frequently asked questions
How do I calculate my baby's age in weeks?
Count the days since birth and divide by 7. A baby born 45 days ago is 6 weeks and 3 days old. Babies are commonly described in weeks until about 3 months.
How are baby months counted?
Your baby turns one month older on the same day of the month as their birth date: born on March 10 means 1 month on April 10, 2 months on May 10, and so on. If that day doesn't exist (born on the 31st), the last day of the shorter month is used.
How many weeks is a 3-month-old?
About 13 weeks. Because months have 28 to 31 days, 3 calendar months is 89–92 days, which is 12.7–13.1 weeks.
When is my baby's 100th day?
The 100th day celebration is usually counted as 100 days after birth, which is shown in the milestone table. Some traditions count the birth day as day 1, which makes it one day earlier.
Should I use corrected age for a premature baby?
For babies born before 37 weeks, doctors use corrected (adjusted) age to judge development until about age 2. Use the corrected age calculator to subtract the weeks your baby was born early.
Is the half birthday 6 months?
Yes, the half birthday is 6 calendar months after birth, for example September 15 for a baby born on March 15.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.
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