How to Calculate Age From Two Dates

Figure out someone's age by using the birth date.

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.

  • Paper
  • Pencil
  • Calculator

1 Calculate Age from Birthdate

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

2 Get the birth date

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.

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

3 Write down the current year

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.

Compare today's date with their birthday.

4 Subtract one from your answer of 59

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.

Use computer programs to verify the answer.

5 Verify your calculation

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.

  • If you need to know the age in months and days, use an online calculator to save you time and frustration. If you only need to know the age in years, do it as a simple subtraction problem.

Karen Worthy has been a freelance writer since 2007. She has written on topics ranging from personal finance and technology to education and parenting. Over the years, she has worked as a technical engineer, general manager and tax consultant. She has a Bachelor of Science in mechanical engineering from the University of Texas.