This calculator uses the most common age system, where a person’s age increases on their birthday. For instance, someone who is 3 years and 11 months old has an age of 3. They will turn 4 on their next birthday, which is one month away. This is the standard system used in most Western countries.

However, the way we count age varies across cultures. In some systems, age is counted by including or excluding the current year. For example, a twenty-year-old is considered to be in their twenty-first year of life. In one traditional Chinese system, a person is born at age 1, and their age increases on the day of the Chinese New Year, not their birthday. This means a baby born one day before the New Year would be considered 2 years old just two days later.

A Note on Month Calculations

You may sometimes find the month and day results confusing, particularly when the dates fall at the end of a month. This is due to the uneven number of days in each month.

For example, calculating the age from February 28 to March 31 can be interpreted in two valid ways:

Counting from Feb. 28 to Mar. 28 as one month gives a result of 1 month and 3 days.

Treating both Feb. 28 and Mar. 31 as the end of their respective months gives a result of exactly 1 month.

Both methods are logically sound. This situation can also occur between other dates like April 30 to May 31. For clarity and consistency, our calculator uses the first method in all its calculations.