How Age is Calculated
The age of a person can be counted differently in different cultures. This calculator is based on the most common age system used globally.
The Western Age System
In this standard system, age increases precisely on a person's birthday. For example, the age of a person who has lived for 3 years and 11 months is considered 3. Their age will officially increase to 4 on their next birthday, one month later. Most western countries use this age system for official and legal purposes.
Alternative Age Systems (Traditional Methods)
In some cultures, age is expressed by counting years with or without including the current year. For example, a person who is "twenty years old" in the Western system is considered the same age as a person who is "in their twenty-first year of life" in other systems.
In one of the traditional Chinese age systems, people are considered to be born at age 1, and their age increases at the Traditional Chinese New Year rather than on their biological birthday. For example, if a baby is born just one day before the Traditional Chinese New Year, 2 days later, the baby will be considered 2 years old, even though they have only been alive for 2 days.
Month and Day Calculation Edge Cases
In some situations, calculating the exact months and days can be confusing, especially when the starting date is at the end of a month. For example, we count February 20 to March 20 as exactly one month.
However, there are two ways to calculate the age from February 28, 2022, to March 31, 2022:
- If we consider February 28 to March 28 to be exactly one month, then the total result is one month and 3 days.
- If we consider both February 28 and March 31 as "the end of the month," then the result is exactly one month.
Both calculation results are mathematically reasonable. Similar situations exist for dates spanning April 30 to May 31, May 30 to June 30, etc. The confusion arises strictly from the uneven number of days in the Gregorian calendar months. In our calculations, we use the former method (calculating exact days past the calendar date match).