I have to admit, the title of this post is a little bit misleading because there is no direct way to input military time into Excel. If you try to input "1300" as 1:00PM, Excel has no way to know that you're entering a time as opposed to a number. In order for Excel to recognize your input as a time and not 1,300 you must enter a colon and enter as "13:00". Basically, formatting the cells for dates and times only affects how the contents of the cell is displayed and not how the information is entered. So if you enter the military time with a colon and format the cell as Time then 1300 will be converted to 1:00PM.
Here's why: Excel stores dates and times as days and fractions of a day, where the number 1 equals January 1st, 1990. Entering 1300 into a cell leads Excel to interpret that as the 1300th day since January 1st, 1900 at 12 midnight. Enter 1300 into a cell and format it as Time. Notice the value displays this: 7/23/1903 12:00:00 AM. Interesting, no?
Going back to the original question, how to input military time into Excel, my suggestion is this: entering a colon while inputting the military time is extra work. We always want to make data entry fast and painless as possible. So let's use a formula that will enable us to enter military time as 1300 but then display the regular time. If we input the value of 1300 in cell A1, enter the following formula into cell B1:
In the picture above, you can see the how the military time is entered and the formula converts it to standard time. This post was inspired by a question from a reader on our Excel Spreadsheets Help Facebook page.