Babies, toddlers & kids
Age in Months Calculator
How many months old is your child, or how many months old are you? Enter a birth date to get the exact age in months and days, plus weeks, years and months, and the date of the next month-birthday.
By Sandeep · Last updated November 2026
How many months old?
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Enter a birth date and press Calculate Age in Months.
Age in months
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How to Calculate Age in Months
To calculate age in months by hand, find the age in years and months first, then convert the years:
- Find the age in years, months and days from the birth date to the current date. Our guide to calculating age by hand shows the borrowing method.
- Multiply the years by 12.
- Add the remaining months. Keep the leftover days if you need them, for example 41 months and 9 days.
The age in months calculator above does all three steps and counts the real length of every month, including February in a leap year, so the days are exact.
How Many Months Old Is a 1, 2, 3, 4 or 5 Year Old?
A child turns a whole number of years at exactly 12, 24, 36 months and so on. Use this chart to convert age in years to months:
| Age in years | Age in months | Covers |
|---|---|---|
| 1 year old | 12 months | 12 to 23 months |
| 1½ years old | 18 months | 18 to 23 months |
| 2 years old | 24 months | 24 to 35 months |
| 3 years old | 36 months | 36 to 47 months |
| 4 years old | 48 months | 48 to 59 months |
| 4½ years old | 54 months | 54 to 59 months |
| 5 years old | 60 months | 60 to 71 months |
| 13 years old | 156 months | 156 to 167 months |
So a 3 year old is between 36 and 47 months old, depending on how long ago their third birthday was. To get the exact number, use the calculator.
How Many Weeks Is a Baby in Months?
A month is about 4.35 weeks on average, because most months have 30 or 31 days. In the first year, parents and doctors often switch between weeks and months:
| Age in months | Approximate weeks |
|---|---|
| 1 month old | about 4 weeks |
| 2 months old | about 8–9 weeks |
| 3 months old | about 13 weeks |
| 4 months old | about 17 weeks |
| 6 months old | about 26 weeks |
| 9 months old | about 39 weeks |
| 12 months old | about 52 weeks |
The weeks shown in the calculator result are exact, based on the actual birth date.
Age in Months Examples
- Born 14 March 2025, today is 31 October 2026: 1 year, 7 months and 17 days, so 12 + 7 = 19 months and 17 days old.
- Born 30 June 2022, age on 15 January 2026: 3 years, 6 months and 16 days, so 36 + 6 = 42 months and 16 days old.
- Born 1 September 2020, age on 1 March 2025: exactly 4 years and 6 months, so 54 months old, the answer to “how many months old is 4½”.
Enter any of these dates in the calculator above to check the working.
Age in Years and Months vs Total Months
Both formats describe the same age. “3 years and 5 months” is easier to say, while “41 months” is easier to compare, because you do not have to think about years at all. That is why baby milestone charts, pediatric growth charts and many infant tests use total months, while school forms and test records for older children use years and months, written 3;5. The calculator gives you both, so you can copy whichever your form asks for.
Why Age in Months Matters for Babies and Toddlers
Young children change so quickly that a few months make a big difference. That is why child age is usually counted in months until about age 2 or 3:
- Milestones: skills such as sitting, walking and first words are tracked by month.
- Check-ups and growth charts: well-child visits and weight and height charts use age in months.
- Developmental tests: infant and toddler assessments, such as the Bayley-4 (16 days to 42 months), are scored by age in months. See our test age ranges.
- Clothing and toys: sizes like 6–12 months and 18–24 months are based on age in months.
If your baby was born before 37 weeks, doctors usually use corrected age for milestones. Find it with our corrected age calculator.
Age in Months for Adults
Age in months is not only for babies. “How many months old am I?” is a fun way to see your age from a new angle: a 30-year-old has lived 360 months. Months are also used for age verification on some forms, insurance and retirement planning, where your exact age in months can decide eligibility.
For your exact age in years, months and days, use our main chronological age calculator.
Age in Months Calculator FAQs
How many months old am I?
Enter your date of birth in the calculator above. It shows your exact age in months and days. By hand, multiply your age in years by 12 and add the months since your last birthday.
How many months is a 3 year old?
A 3 year old is between 36 and 47 months old. They are exactly 36 months on their third birthday.
How many months is a 2 year old?
A 2 year old is between 24 and 35 months old.
How many months is a 4 year old?
A 4 year old is between 48 and 59 months old. A child who is 4½ is 54 months old.
How many weeks is 4 months old?
About 17 weeks. Because months have 28 to 31 days, the exact number depends on the birth date.
When should I stop counting my child’s age in months?
Most parents and doctors switch to years and months around age 2, and to whole years after about age 3. Developmental tests may still use months for longer.