To work out someone's age as a decimal you need to work out the number of days between their birth and today. Once you have the number of days then you can divide it by 365.25, which is the number of days in a year.
We use 365.25 to take into account leap years.
Decimal age is your age expressed as a single number with a decimal point, such as 25.75 years. It represents your age as a continuous value rather than rounding down to whole years, making it useful in contexts where precision matters.
Decimal age is calculated by dividing the total number of days between your birth date and today by 365.25 (the average length of a year accounting for leap years). The result gives you your age as a precise decimal number.
Decimal age is commonly used in medical research, pediatric growth charts, epidemiology, and psychological testing. It allows researchers to compare individuals at precisely the same stage of development rather than grouping them into broad annual age categories.
The value 365.25 is used to account for leap years, which add one extra day every four years (on average, 0.25 days per year). Using 365.25 gives a more accurate average year length and produces more consistent decimal age results over time.
Decimal age and chronological age measure the same thing, the time elapsed since birth, but express it differently. Chronological age is typically stated in whole years, while decimal age provides a continuous, fractional representation that is especially useful in scientific and clinical settings.