The Excel function: NOW
Returns the serial number of the current date and time. If the cell format was General before the function was entered, Excel changes the cell format so that it matches the date and time format of your regional settings. You can change the date and time format for the cell by using the commands in the Number group of the Home tab on the Ribbon.
The NOW function is useful when you need to display the current date and time on a worksheet or calculate a value based on the current date and time, and have that value updated each time you open the worksheet.
Note If the NOW function does not update cell values when you expect it to, you might need to change settings that control when the workbook or worksheet recalculates. These settings can be changed in Control Panel for the Excel desktop application.