Age & Birthday Calculator
Use this date of birth calculator to easily calculate age. Our DOB calculator determines the time interval between two dates, providing a full breakdown from years down to seconds.
Calculate Age
Calculated Age / Duration
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Precise Calculation
Calculates the exact duration between two dates, down to the second, based on the common age system.
Cultural Age Systems
Learn about different ways age is counted around the world, such as the traditional Chinese system.
Handles Ambiguity
Understands and consistently calculates intervals for tricky end-of-month dates.
Understanding Age Calculation
The Common Age System
This calculator uses the most common age system, prevalent in Western countries. In this system, age increases on a person's birthday. For example, a person who has lived for 3 years and 11 months is considered to be 3 years old, and their age will increase to 4 on their next birthday one month later. For more versatile time interval calculations, try our Duration Calculator.
Handling Date Ambiguity
Calculating time intervals can be confusing due to the uneven number of days in months. For instance, calculating the time from Feb. 28 to Mar. 31 can be interpreted in two ways. This calculator uses a literal method, where counting from Feb. 28 to Mar. 28 is considered one full month. This results in an interval of one month and 3 days. The alternative method would consider both dates as the end of the month, resulting in an interval of exactly one month. Our calculator provides a more direct duration based on the calendar day.
Alternative Age Systems
Counting Years of Life
In some cultures, age is expressed by counting years of life rather than exact time since birth. A person who is twenty years old is considered the same age as someone who is in their twenty-first year of life. This system focuses on the ordinal year of life.
Traditional Chinese Age System
One traditional Chinese age system differs significantly from the Western method. In this system, a person is considered age 1 at birth. Their age then increases by one year at the start of the Traditional Chinese New Year, not on their birthday. For example, a baby born just one day before the Chinese New Year would be considered age 2 only two days later, despite being just a couple of days old in Western terms.