For infants, toddlers & early intervention
Age in Months Calculator
Exact age in months and days.
For milestones, growth charts and tests.
Young children are usually described by their age in months, not years. Enter a date of birth and the date you need, and get total months, leftover days, decimal months and the years;months form test manuals use.
- Total months + leftover days
- Decimal months to 2 places
- 30-day or calendar borrowing
- Copy & print the result
How many months is that?
Enter a date of birth to see the age in months.
- Test notation
- Total days
- Method
Show calculation steps
Three steps
How to use the age in months calculator
Two dates in, months out.
- Enter the date of birth.
- Enter the “age on” date. It defaults to today. Change it to the test date or any other date.
- Press Calculate months. You get total months and days, decimal months, total weeks and years;months.
Worked example
Turning years into months
A child born on June 15, 2018 and tested on October 27, 2025.
Count the age
The age is 7 years, 4 months and 12 days.
That is the same age our main calculator gives, written as 7;4.12.
Convert to months
7 years × 12 = 84 months, plus 4 months = 88 months, plus 12 days.
As a decimal: 88 + 12 ÷ 30.44 = 88.39 months.
Where months matter
Why use age in months?
Small age gaps matter a lot in the first few years, so ages are tracked in months.
- Developmental milestones: checklists for babies and toddlers are grouped by months, like 9, 12 or 18 months.
- Growth charts: weight, length and head size for young children are plotted by age in months.
- Early childhood tests: many infant and toddler assessments report age and norms in months.
- Everyday questions: parents often describe a toddler as 20 or 30 months old rather than “almost 2”.
Still unsure?
Questions people ask
Tap a question to open it.
How do you calculate age in months?
Work out the age in years, months and days first, then multiply the years by 12 and add the months. The leftover days stay as days, or can be turned into a decimal by dividing them by the average month length (about 30.44 days).
What does decimal months mean?
It shows the leftover days as part of a month. 88 months and 12 days is about 88.39 months. It’s handy for spreadsheets and graphs, but most test manuals use whole months and days.
Until what age are children described in months?
Usually until about 2 or 3 years old. After that, years and months (like 3;6) is more common.
Should I use corrected age for a premature baby?
For babies born before 37 weeks, many guidelines use corrected age for milestones until about age 2. Use our corrected age calculator to find it.
Is the date of birth stored anywhere?
No. The calculation runs entirely in your browser and nothing is sent or saved.