From time to time, people approach me with an Excel problem that looks easy to calculate while, unfortunately, there’s no straightforward solution to it. The problem is calculating the difference (in hours) between two date-time formatted cells.

**Example:**

Cell A1: 2/15/2012 10:00:00 AM

Cell B1: 2/18/2012 08:00:00 PM

What is the elapsed time between both dates (in hours)?

You can get the answer by using the below formula in cell C1:

= INT(B1-A1)*24+(((B1-A1)-INT(B1-A1))/0.04166666)

**The result will be: 82 HRS**

**Formula rationale:**

Excel stores all dates as integers and all times as decimal fractions. With this system, Excel can add, subtract, or compare dates and times just like any other numbers. Times are stored as decimal numbers between .0 and .99999, where .0 is 00:00:00 and .99999 is 23:59:59. So, an hour is about 0.041666 of the 0.99999.

Hence, with multiplying the integer part of the date serial number by 24 (to get number of hours for the whole elapsed days) and adding the result to the number of hours represented in the fraction part (the fraction part divided by 0.014666) you get the total number of elapsed hours between both dates.