Excel treats dates and times as special types of numeric values. Dates and times are values
that are formatted so that they appear as dates or times. If you work with dates and times,
you need to understand Excel’s date and time system.
Entering date values –
Excel handles dates by using a serial number system. The earliest date that Excel under-
stands is January 1, 1900. This date has a serial number of 1. January 2, 1900, has a serial
number of 2, and so on. This system makes it easy to deal with dates in formulas. For exam-
ple, you can enter a formula to calculate the number of days between two dates.
Most of the time, you don’t have to be concerned with Excel’s serial number date system.
You can simply enter a date in a common date format, and Excel takes care of the details
behind the scenes. For example, if you need to enter June 1, 2019, you can enter the date
by typing June 1, 2019 (or use any of several different date formats). Excel interprets your
entry and stores the value 43617, which is the serial number for that date.
Entering time values –
When you work with times, you extend Excel’s date serial number system to include deci-
mals. In other words, Excel works with times by using fractional days. For example, the
date serial number for June 1, 2019, is 43617. Noon on June 1, 2019 (halfway through the
day), is represented internally as 43617.5 because the time fraction is added to the date
serial number to get the full date/time serial number.
Again, you normally don’t have to be concerned with these serial numbers or fractional
serial numbers for times. Just enter the time into a cell in a recognized format. In this
case, type June 1, 2019 12:00.