Calculation of Decimal Age

year = YEAR(date) - 1900

month = MONTH(date)

day = DAY(date)

A = (12 * (year)) + (month) + 9

B = INT(A / 12)

C = A - (12 * B)

D = (B - 1) - (4 * INT((B - 1) / 4))

number of days for date from 1/1/1900 =

= INT((365.25 * B) + (30.6 * C) + (day) - (0.25 * D) - 305.8)

decimal age =

= ((number of days for end date from 1/1/1900) - (number of days for birthday from 1/1/1900)) / 365.25

For patients with birthdays before 1/1/1900, add 36,525 (365.25 * 100) to the total number of days:

decimal age =

= (36525 + (number of days for end date from 1/1/1900) - (perceived number of days for birthday from 1/1/1900)) / 365.25