Returns whether the given value is an #N/A error ("not available"). As the NA function returns 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:

The IFNA function is used to return a specific value if a value is an #N/A error, or the value itself otherwise. This formula returns 500, 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 formula above returns TRUE if Value2 is 0 or blank, resulting in a #DIV/0! error ("division by zero"), but it returns FALSE if the value resulting from the Value1 / Value2Value1 / Value2 cannot be found in the lookup array.

ISNA and arrays

Applying ISNA to an array yields a logical array with the same size as the original array, where TRUE elements indicate that the corresponding element in the original array is an #N/A error and FALSE elements indicate the opposite.

This formula returns { TRUE, FALSE }{ TRUE; FALSE }, indicating that the first array element is an #N/A error and the second array element is not (it is a #DIV/0! error):

(The formula above requires that Value2 is 0 or blank.)