Excel: Mathematical operations on date and time

You can perform such arithmetic operations as addition or subtraction not only on numbers but also on dates. In this lesson, I will show you a few examples of how you can do it. 

Calculating the number of days between two dates

Example 1:

If you want to perform addition or subtraction on dates, first, you need to save them in separate cells. Let it be cell A1 and cell A2.

A1 = January 10, 2014 15:15:00

A2 = February 12, 2014

When a date includes time other than midnight (24:00:00 is the default time) then the number of days that are returned will be reduced by one. The following examples show ways to ignore time and use only the date part. 

Example 2:

= DAYS(A2A1)

returns 33.

In this example, the DAYS function returns the number of days between two dates. 

Example 3:

= INT(A2) - INT(A1)

returns 33.

The date and time were rounded to the nearest integer (in this case, it means getting rid of the time part, so only a day will be remembered. The time will be set to the default value, which is 24:00:00). 

Adding and subtracting days

Let's use the example from the previous exercise. 

Example 4:

A1 = January 10, 2014

If you want to see what date will be 33 days after the date of January 10, 2014, you can add to that date the number 33.

Look at the following formula: 

= A1 + 33

The result will be February 12, 2014. You can also check what date was 33 days before the date of February 12, 2013

A2 = February 12, 2014

= A2 - 33

The result is January 10, 2014.