An age in months is the number of whole calendar months since the date of birth, plus the days left over: count the "month birthdays" — the same day of each month — that have passed, then the days since the last one. A baby born on March 10, 2025 is 19 months and 20 days old on October 30, 2026.
The calculator counts real calendar months, never 30-day blocks, gives a decimal figure for charts and forms, and lists the dates of the next month birthdays.
Worked example
Date of birth: March 10, 2025Count to: October 30, 2026
Months old on Oct 30, 2026: 19 months, 20 days
March 10, 2025 to October 10, 2026 is 19 whole months, and October 10 to October 30 adds 20 days — about 19.6 months.
Open this example in the calculator →How to use the Age in Months Calculator
- Enter the date of birth.
- Leave "Count to" as today, or pick the date you need the age for — a check-up or a form.
- Read the age in whole months and days, and the decimal months.
- See the next month birthdays below, with their dates and weekdays.
How to calculate age in months
- Count the years and multiply by 12. A child born March 10, 2025 had their first birthday on March 10, 2026: 1 × 12 = 12 months.
- Add the whole months since the last birthday. From March 10 to October 10 is 7 months, making 19.
- Add the days since the last month birthday. From October 10 to October 30 is 20 days.
The answer is 19 months and 20 days. Dividing a day count by 30 or 30.44 instead gives a slightly different answer that drifts with the length of the months — it is an average, not a calendar.
When do people stop counting in months?
Babies' ages are usually given in weeks for the first couple of months, in months up to 2 years, and in years and months after that. Doctors and growth charts often keep using months until about 24 months — "18 months" says much more about a toddler's development than "1 year". For premature babies, the baby age calculator gives the corrected age too.
Decimal months
Some forms and growth charts ask for an age as a decimal. The calculator divides the days since the last month birthday by the length of the current month (the days from one month birthday to the next), so 19 months and 20 days in a 31-day stretch is 19 + 20 ÷ 31 ≈ 19.6 months.
Birthdays on the 29th, 30th or 31st
Not every month has a 31st. When the month is too short, the month birthday falls on the 1st of the following month: a baby born on January 31 is 1 month old on March 1 (February has no 31st) and 2 months old on March 31. The months and days in the result follow the same rule, so they always agree with the table of month birthdays.
Frequently asked questions
How many months old is my baby?
Enter the date of birth and the calculator counts the whole calendar months and leftover days to today. For example, a baby born on March 10, 2025 is 19 months and 20 days old on October 30, 2026.
How many months is 2 years old?
24 months. 18 months is 1½ years, and 30 months is 2½ years.
Is a month counted as 30 days?
No. The calculator counts real calendar months — from a date to the same date the next month — so a month can be 28, 29, 30 or 31 days.
What is my age in months as a decimal?
The whole months plus the fraction of the current month that has passed. The calculator shows it to one decimal place.
What if the birth date is the 31st?
In months without a 31st, the month birthday falls on the 1st of the next month. Born January 31, a baby is 1 month old on March 1 and 2 months old on March 31.