Returns an #N/A error ("not available"). As the ISNA function returns whether its parameter is an #N/A error, ISNA ( NA ()) ISNA ( NA ()) returns TRUE.

Lookup functions like XLOOKUP return #N/A errors when a value cannot be found. The ISNA function may be used to detect the #N/A error specifically.

This formula returns TRUE, because the sought value, 10, is not part of the { 20, 30 }{ 20; 30 } lookup array given to XLOOKUP:

ISERR is the opposite of ISNA, meaning that it detects all errors except for #N/A errors. Consider this formula:

The preceding formula returns TRUE if Value2 is 0 or blank, resulting in a #DIV/0! error, but it returns FALSE if the value resulting from the Value1 / Value2Value1 / Value2 calculation cannot be found in the lookup array.