Learn how to figure out dates using formulas in Excel

What dates mean to Excel

There’s a difference between what dates mean to you and what they mean to Excel.

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To you, 8/22/2010 is a month, day, and year.

To Excel, 8/22/2010 is serial number 40412.

In this lesson you’ll learn how Excel’s view of dates makes it possible to do date arithmetic, and how to enter dates in a format that Excel can understand.

Learn how to figure out dates using formulas in Excel

The calendar starts in 1900

Dates are stored in Excel as serial numbers starting with 1, which represents January 1, 1900. That’s when the Excel calendar starts.

Each day after that adds one number to the sequence. For example, January 2, 1900 is stored as 2.

That means if you type 8/22/2010, Excel stores the date as 40412 — or 40411 days from January 1, 1900.

Learn how to figure out dates using formulas in Excel

The calendar starts in 1900

Storing dates as serial numbers makes it possible for Excel to do date arithmetic.

To find the number of days between two dates, for example, Excel subtracts one serial number from another.

Learn how to figure out dates using formulas in Excel

How Excel recognizes dates

Whether you type 8/22/2010, 22-Aug-2010, or even August 22, 2010, it’s all stored as serial number 40412.

The exception is if you use a format that Excel doesn’t recognize as a date.

For example, if you typed August-22,2010 or 8,22,10, Excel would store that information as plain text, not a serial number.

Learn how to figure out dates using formulas in Excel

How Excel recognizes dates

Here’s how you can change the format—or see some of the other ways you can use slashes or hyphens to format dates.

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Select Date in the Category list.

Select a date format in the Type list.

Right-click a cell with a date in it, and choose Format Cells. Then you can: