Calculate your age by finding the difference between your DOB and the current date. What we are discovering is how much time has crossed since your date of birth. The date/age calculator can be used not only to determine the number of days you have but also to calculate the number of days, weeks, and months before an event, for example, to calculate the number of days left before your birthday, count by Christmas flip, etc. You can also use the YEAR function to calculate the age in Excel in a specified date range. YEARFRAC calculates a decimal number that represents the fraction of a year between two dates.