IFERROR & error traps — Excel guide
Error handling with intent: trap the failures you EXPECT, let real bugs stay loud. The difference between friendly and dangerous is which errors you silence.
IFERROR
Show a fallback when a calculation errors — any error at all.
- Wrap the PIECE you expect to fail, not the whole formula — blanket IFERRORs turn bugs into silent zeros.
- Never wrap a total: a broken source showing as 0 is the expensive kind of lie.
- Fallback chains work: IFERROR(lookup in new table, lookup in legacy table).
- 0 vs "" as fallback changes downstream AVERAGEs and arithmetic — choose for the consumer.
IFNA
Trap ONLY #N/A — real mistakes (#REF!, #NAME?) still surface.
- The better default around lookups: a missing value is expected, a misspelled function is not.
- XLOOKUP's if_not_found argument replaces this wrapper entirely.
ISERROR
TRUE/FALSE: is this an error? For tests, formats, and counts.
- As a conditional-formatting rule (=ISERROR(A1)) it paints every error red.
- ISNA checks only #N/A; ERROR.TYPE returns which error by number.
- Sum around unfixable errors: AGGREGATE(9, 6, range).
- Diagnose before trapping: Evaluate Formula, or F9 on a selected fragment.