How to Calculate Chronological Age?

Chronological age is something that most people have never heard of and most people will never use it. It is vitally important to teachers and other professionals involved in the assessment (testing) of individuals. Education professionals are going to be primarily concerned with chronological age as it relates to students in a school system. Students can be tested for a variety of reasons including special education services or it might simply be to allow teachers to get a better feel for what methods are working in the classroom.

So what is chronological age? Chronological age is simply the exact age of a person all the way down to the precise day. More on this in a just a little bit. Chronological age is important in assessment because it allows education professionals to use the data they gain from testing and convert it into various types of scores that are used for educational placement or curriculum guides. Now let us see how chronological age is calculated.

It is actually quite easy to calculate chronological age once you have done it a few times. The best way to learn is by looking at examples or questions regarding chronological age. Let us look at are first question.

If John was born on October 12, 1987, and he is being tested on August 5, 1999, what is his chronological age on the day he is being tested?

Here is the formula: Year Month Day (Test Date) - Year Month Day (Birth Date)= Chronological Age

Now we will use the formula above to answer the first question.

1999 8 5 (Test Date) - 1987 10 12 (Birth Date) = 11 years, 9 months, 23 days (see explanation below)

Here is how this would look if you were to work the above problem out on paper.

1999 8 5

- 1987 10 12

After you have put it on paper it is simple subtraction with a few key differences. Since 12 cannot be subtracted from 5 we are going to have to borrow. Pay attention closely. We are going to borrow from the months column, making the 8 a 7. Now when you borrow from the month column you are actually borrowing a month, or 30 days. You will add 30 days to the 5 days we already have making it 35 minus 12. This is how we get 23 days.

Now we have a 7 minus 10 in the months column so we are going to have to borrow from the years column. We are actually going to borrow an entire year (12 months), making the 1999 a 1998. We add 12 months to the 7 we have in the months column, making it 19 minus 10. This is how we get 9 months. Finally, in the years column we now have 1998 minus 1987 giving us 11 years.

After all the borrowing is said and done the above problem would look like this.

1998 19 35

-1987 10 12

11 09 23

Now let us do one more just to make sure that everybody understands this concept.

If Janie was born on May 6, 1996, and she was tested on July 8, 2007, what is her chronological age on the day she is being tested?

We set up are problem based on the formula above.

2007 7 8

- 1996 5 5

The key difference in this one is that nothing has to be carried or borrowed. It is real simple subtraction.

The final answer is 11 years, 2 months, 3 days. 2007 - 1996 = 11 years. 7 (July) minus 5 (May) = 2 months. 8 - 5 = 3 days

You should now be able to calculate chronological age.