Converting Time Notation to Decimal Notation

Excel internally stores date and time values as floating-point numbers. The portion of the number to the left of the decimal point represents days elapsed since either January 1, 1900 or 1904 (depending on how your copy of Excel is configured). The portion of the number to the right of the decimal point represents the portion of a full day represented by the date and time.

Knowing this, you can easily convert a number from its time notation to its decimal equivalent. For instance, if you have an elapsed time value that represents 8:30, you can easily convert it to 8.5 (eight and a half hours) by multiplying the time value by 24.

To give another example, let's say that you have a beginning time in cell A3 and an ending time in cell B3. In cell C3 you place the following formula:

=B3 - A3

The result in cell C3 is the elapsed time, which is the difference between the beginning and ending times. This approach only works if the beginning time (A3) is less than the ending time (B3). This won't always be the case, particularly if the starting time is late one one day and the ending time is early on a later day. If you think you might have start and end times that occur on two days, then it is best to use a formula such as this:

=MOD(B3-A3,1)

Once you have the elapsed time, then in cell D3 you could then place the following formula:

= C3 * 24

The result in D3 is a decimal representation of the number of hours in cell C3. You can format the cell as you would any other number value so that it displays the number of decimal places desired. If you prefer to limit the number of decimal places in the result, right off the bat, you could instead use the following formula in cell D3:

=ROUNDUP(C3 * 24, 1)

This formula multiples C3 by 24 to convert to a decimal value, but then rounds the result to a single decimal place.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (10700) applies to Microsoft Excel 2007, 2010, 2013, 2016, 2019, and 2021. You can find a version of this tip for the older menu interface of Excel here: Converting Time Notation to Decimal Notation.