Figuring out a person's age requires that you know the date of birth and the current date. Many forms asks users to fill in their birth date, but not their age. Calculate the age with basic math skills.

Calculate Age from Birthdate

Step 1

Write down the date of birth on a sheet of paper.
Write down the date of birth on a sheet of paper.

Get the birth date of the person in question. Write it down on a sheet of paper in the format of month/day/year. For example, someone born on July 17, 1952 would have a written birth date of 7/17/1952.

Step 2

Use a calculator if you are not comfortable subtracting on your own.
Use a calculator if you are not comfortable subtracting on your own.

Write down the current year and subtract the person's year of birth. For example, if the current year is 2011, subtract 1952 from 2011. You can either do this by hand with a pencil and paper, in your head or use a calculator. In this example, you should get an answer of 59.

Step 3

Compare today's date with their birthday.
Compare today's date with their birthday.

Subtract one from your answer of 59 if the birthday comes after the date on which you're doing the calculation. For example, if you're making the calculation on March 4, 2011, someone born on July 17, 1952 would only be 58 years old since the birthday has not passed.

Step 4

Use computer programs to verify the answer.
Use computer programs to verify the answer.

Verify your calculation by using a hand-held or online calculator or a computer program like Microsoft Excel. Type the dates in separate cells and subtract one cell from the other.