Bookkeepers, project managers, HR departments and more use the Excel Date & Time functions WEEKNUM, ISOWEEKNUM, WORKDAY, WORKDAY.INTL to calculate time. Here's how.

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.

For example, the DATEVALUE function in the Date & Time category also returns a numeric value, which is the serial representation of a character string.