In the example, the formula is:
B5 contains a date value for January 5, 2016.
The DAY function returns the number 5 representing the day component of the date.
you might use the DAY function to extract a day number from a date into a cell.
Get day from date
If you need to extract the day from a date, you can use the DAY function. The date must be in a form that Excel recognizes as a valid date. In the example shown, the formula in cell B5 is: =DAY(B5)
