The age of a person can be counted differently in different cultures. This calculator is based on the most common age system. In this system, age increases on a person's birthday. For example, the age of a person who has lived for 3 years and 11 months is 3, and their age will increase to 4 on their next birthday one month later. Most western countries use this age system.

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 is the same age as another person who is in their twenty-first year of life. In one of the traditional Chinese age systems, people are born at age 1 and their age increases up at the Traditional Chinese New Year rather than their birthday. For example, if one baby is born just one day before the Traditional Chinese New Year, 2 days later, the baby will be 2 even though he/she is only 2 days old.

In some situations, the months and day result of this age calculator may be confusing, especially when the starting date is the end of a month. For example, we count Feb. 20 to Mar. 20 to be one month. However, there are two ways to calculate the age from Feb. 28, 2022 to Mar. 31, 2022. If we consider Feb. 28 to Mar. 28 to be one month, then the result is one month and 3 days. If we consider both Feb. 28 and Mar. 31 as the end of the month, then the result is one month. Both calculation results are reasonable. Similar situations exist for dates like Apr. 30 to May 31, May 30 to June 30, etc. The confusion comes from the uneven number of days in different months. In our calculations, we use the former method.

This age calculator uses 2 similar but slightly different methods to calculate age. One method is used to give age in years, months and days, and also months and days. The other method is used to very precisely calculate age in total days only.

When calculating age to the detailed level of days it's important to remember that not all months have the same number of days. Also, while a year has 365 days, a leap year has 366 days.

When you calculate age in terms that include years, this calculator provides the answer in common terms. For example, a teenager might say he is 15 years old rather than saying he's 12 normal years old plus 3 leap years old. This age calculator uses the same assumption -- although we know years may have different lengths, we generalize between regular years and leap years, and call them equal.

The same is true for months. If a baby is 7 months old, the parents would not say she is 4 months that are 31 days long, plus 2 months that are 30 days long, plus 1 month that is 28 days long. We typically generalize across months of different lengths, and count them all equal as general months.

The age calculator finds age in terms that are commonly used, calling all years equal and all months equal. When calculating days however, the calculator uses a function to find the precise number of days between dates.

If you wanted to know how many days you've been alive you need to account for extra days in leap years. You also need to know the total number of months with 31 days, total months with 30 days, and total months with 28 days.

The age calculator uses a function that recognizes how many leap years are in a given time span. It also calculates the specific number of days in a partial year. For example, if you were born on March 5 and today is June 7, the calculator finds the exact number of days that occur between those dates.

Your age in total number of days is calculated as:

Number of years, x, with 365 days = 365x plus
Number of years, y, with 366 days = 366y plus
Number of days in the remaining partial year

This calculator assumes the start date is day 0 and begins counting one full day after day 0. For example if you input the dates 03/15/2022 and 3/18/2022 into the calculator you will get a total age of 3 days. Day 1 is the 16th, day 2 is the 17th, and day 3 is the 18th. The 15th is not counted in the tally of days.