Summary
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)
Generic formula
=DAY(date)
Explanation
The DAY function takes just one argument, the date from which you want to extract the day. In the example, the formula is:
=DAY(B5)
B5 contains a date value for January 5, 2016. The DAY function returns the number 5 representing the day component of the date.
Note that you can use DAY to extract the day from a day entered as text:
=DAY("1/5/2016")
But this can produce unpredictable results on computers using different regional date settings. In general it's better (and more flexible) to supply an address to a cell that already contains a valid date value as the argument for DAY.
