The Excel ISBLANK function returns TRUE if cell value is blank and False if the cell is not blank, and it is also an information function.

Excel has over 475 formulas in its Functions Library, but we've selected the most popular, from date and time functions to mathematics and simple data manipulation.

The four functions covered here—ISOWEEKNUM, WEEKNUM, WORKDAY, WORKDAY.INTL—are complicated, so we’ll walk you through detailed instructions and examples.