Excel represents dates and time as numbers, specifically known as date serial numbers or date-time serial numbers. When you view a date in Excel, you are actually seeing a numerical value that has been formatted to appear as a date. If you change the cell's format to 'General', the underlying date serial number will be revealed.
The integer component of the date serial number signifies the day, and the decimal portion represents the time. The counting starts from the 1st of January, 1900, which has a date serial number of 1. Be cautious though, Excel dates after the 28th of February, 1900, are actually offset by one day. This anomaly is due to a bug that was intentionally included by Microsoft for compatibility with the then market-leading spreadsheet program, Lotus 1-2-3, which incorrectly treated 1900 as a leap year.
Excel assigns each date a numeric value, starting from the 1st of January, 1900. The 1st of January, 1900, has a numeric value of 1, the 2nd of January, 1900, has a numeric value of 2, and so on. These numeric values are known as 'date serial numbers', which facilitate mathematical operations and usage in formulas.
Time in Excel also uses a serial number format, represented as decimal fractions. For example, 24 hours equate to 1 day, so 24 hours has a time serial number of 1. Likewise, 12 hours has a value of 0.50 as it represents half a day, and 1 hour is 0.41666' as it's 1/24th of a day.
In Excel, you can input various date configurations, and Excel will automatically recognize it as a date, converting it to a date serial number and applying a date format to the cell. For example, dates separated by a forward slash or hyphen will be recognized as dates. However, dates separated with a period or with spaces between numbers will be treated as text.
Similarly, when you enter time, a specific format of at least h:mm is required. The hour and minutes are separated by a colon without spaces on either side. If you enter a time that includes a seconds component, Excel will automatically format the cell in h:mm:ss.
You can also enter dates and times together in the same cell. In this case, Excel will manage the order for you.
Understanding that Excel treats dates and time as serial numbers makes it logical to perform math operations on these values. For example, you can add/subtract days from dates, subtract dates from each other, add times together, and subtract time from each other.
Excel offers shortcut keys for easy manipulation of dates and time. For instance, using Ctrl + ; inserts the current date, and Ctrl + Shift + ; inserts the current time.
There are few things you need to be aware of when working with dates and time in Excel:
Excel also has two date modes: the 1900 date system and the 1904 date system (used for compatibility with Excel 2008 for Mac and earlier Mac versions). In the 1904 date system, dates are calculated using 1st January 1904 as the starting point. You can switch between these systems in the Advanced Options, but do note that the chosen date setting applies to all dates within the workbook, and you should not reference workbooks that use a different date system in formulas.
To become an expert in Excel date and time, you should further explore:
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In conclusion, this guide should provide you with a robust understanding of how Excel handles dates and time, and help you leverage these functionalities in your daily work effectively.