Subtracting dates is similar to subtracting two numbers, except that we borrow 28, 29, 30, or 31 when subtracting day values, and 12 when subtracting month values. This is because 1 year = 12 months, and 1 month = 28, 29, 30, or 31 days depending on the month and the year.. The reason behind the age of 59 1/2 lies in the rules laid down by the IRS regarding IRA withdrawals. If you withdraw funds from a traditional or Roth IRA before reaching age 59 1/2, you may face a 10% early withdrawal penalty on top of income tax on the withdrawn amount. However, once you reach age 59 1/2, you can make penalty-free withdrawals.
Step #1: Select the month and day, and enter the 4-digit year of your date of birth. Or, if using this as an age difference calculator, enter the birth date of the oldest of the two persons on the first line. Step #2: Select the month and day, and enter the 4-digit year of the date you would like to calculate your age as of that date.. 1. How to calculate chronological age. To calculate your chronological age you need to subtract your date of birth from the current date. However, this is easier said than done because different months have a different number of days. February, for example, has 28 days in a normal year and 29 in a leap year.