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Calculate Age in Months

Calculator for the number of months you are old or that have passed since a certain time. The current date is set as the reference date, i.e. the day up to which the calculation is made, but this can be changed. Only full months are counted, fractions of a month are rounded down. Please select a date of birth or any date and adjust the reference date as needed to calculate the age in months.

Birthday: January February March April May June July August September October November December . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 .

Reference date: January February March April May June July August September October November December . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 .



Age in months:

Example: since January 1. 2000 and until March 9. 2026, when this example text was written, 314 full months have passed.

The age of babies and toddlers is sometimes given in months, as specifying months is of course more precise than saying zero years or one year. This is common practice until around the middle of the second year of life, which is the 18th month. The first year of life is from 0 to 1 year, and the second from 1 to 2 years.
Even later on, specifying age in months can be helpful for some purposes, although it is unusual and rather confusing as the sole indication of age. Of course, specifying age in months doesn't always have to refer to the time between birth and the present. It can be used for any period of time of an appropriate length.

Months is not an exact measure of time, as the 12 months of a year can have varying lengths, between 28 and 31 days. February has 28 days in normal years and 29 days in leap years. Four months have 30 days, and seven months have 31 days. The average length of a month is the length of an average year divided by 12. The length of an average year is 365.2421875 days, resulting in an average month length of 30.43684896 days.

The name month comes from the moon, and the length of a month originally corresponded to the interval between two identical lunar phases, such as from full moon to full moon or from new moon to new moon. However, this is 29.53 days, which is less than an average month. The length of a month was therefore adjusted so that a whole number of months fits into one year. Otherwise, our calendars would be very complicated.

Last updated on 03/09/2026. Author: Jürgen Kummer

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