I have a confession: I don't really understand Mountain Time, and at this point, I'm too afraid to ask. I tend just to ask remote coworkers what time it is there—every single time I see them. Unfortunately, the same approach doesn't work in Excel, and failure to convert time successfully can be a financial hazard. So, if you're working with times in your next spreadsheet—time values, time zones, or otherwise—it's essential to learn how to calculate time differences in Excel.The clock's ticking—it has clocks in Mountain Time, right?—so let's get to it. Excel handles time values as fractions of a 24-hour day. If the whole day is represented as the number 1, different times of the day are decimals. For example, 3:00 p.m. would be represented as 0.625 because it's 62.5% of the way through the day. Regardless of the time you entered and whether you entered it as a decimal or a time, it's always a decimal on the back end. Excel can display something labeled as a "time" value in the more familiar hh:mm:ss format, but it exists as a decimal. Always set the cell type to "Time"—and if you see a weird decimal in a place where you put a time, don't worry about it.Basics of time difference calculation include calculating basic time differences and time differences across different days. For basic time differences, add start and end times for an activity, copy the formula [End time] - [Start time], and paste it into the desired cell. Set the cell category to "Time" before adding the formula. To calculate time differences across different days, change the cell format to m/d/yyyy h:mm, enter the correct values, and calculate the difference using the formula (End date & time - Start date & time)*24. Advanced formulas include handling negative time values, converting time differences to specific units, and using the TEXT function for time differences. There are also general principles such as consistent formatting, using built-in functions, avoiding text entries, and using data validation to steer your sheets clear of time difference calculation mishaps. Additionally, Zapier can be used to automate Excel processes across thousands of apps.