Excel has two error detection functions that are almost identical: ISERR and ISERROR. Their syntaxes are identical:
ISERR(value) and ISERROR(value). They will both return True if the value throws an error. The difference is the ISERROR function will detect #N/A errors and ISERR won’t.
Between the Sheets — Excel podcast episode 31: Excel’s secret DATEDIF function
A quick and simple way of finding the number of days, months or years between two dates is Excel’s secret DATEDIF function. When you type it in a worksheet, there’s no popup syntax help to indicate the function exists.