Suppose you want to adjust a project's schedule date by adding two weeks to see what the new completion date will be, or you want to determine how long a single activity will take to complete in a list of project tasks. You can add or subtract a number of days to or from a date by using a simple formula, or you can use worksheet functions that are designed to work specifically with dates in Excel.
![Add or subtract dates - Microsoft Support](https://cdn-ak-scissors.b.st-hatena.com/image/square/50a62e5e1b1c0889cadac97e7ee767f219883893/height=288;version=1;width=512/https%3A%2F%2Fsupport.office.com%2FSocImages%2FSOC_SharingImage_720x405.png)