ISERROR in Apple Numbers: Detect Formula Errors and Protect Calculations

Use ISERROR to ask whether a calculation is an error. It returns the Boolean TRUE for an error and FALSE for a valid result. It does not replace the error with a useful value—that is what IFERROR is for. Apple’s official example demonstrates error checking around division by zero. [A1]

=ISERROR(12/0)

Expected: TRUE because dividing a number by zero produces an error. The exact UI error code for this calculation is deliberately not claimed. [A1, M1]

=ISERROR(any-expression)

ISERROR has one argument and returns Boolean TRUE/FALSE. It does not accept a second fallback argument, and it is not limited to checking spreadsheet cell references. Do not type the placeholder any-expression literally. For a substitute value instead of a Boolean, use IFERROR(expression, replacement) (see Apple’s official example). [A1]

Create a Numbers table named Orders with four columns (A:D), one header row, and these cells:

Enter each formula in a different empty result cell in column D (for instance, D2:D6), so it does not overwrite input data.

These are expected outputs. The two division-by-zero cases follow Apple’s documented condition; arithmetic and Boolean classification were independently reasoned. [A1, M1]

To show a warning when a unit price cannot be calculated, put this formula into D3, the result cell for row 3:

=IF(ISERROR(A3/B3),"Enter a nonzero unit count",A3/B3)

Expected: Enter a nonzero unit count. The IF branch shows explanatory text instead of the invalid quotient. Apple’s own documentation demonstrates this nested IF(ISERROR(...),...,...) pattern with division by zero. [A2, M2]

A shorter alternative for a numeric result is:

=IFERROR(A3/B3,0)

Expected: 0 because the denominator is zero. If B3 changes to 5, the expected result becomes 9. Choose a text message if a zero could mislead a reader into believing the calculated price really was zero. [A2, M2]

For an audit of the recovery result, try:

=ISERROR(IFERROR(A3/B3,0))

Expected: FALSE: IFERROR supplies a valid replacement number, so the outer ISERROR no longer sees a formula error. This nested example is an independent composition of the two documented functions and has not been natively tested. [A1, M3]

A test of ISERROR(A3/B3) does not repair a separate formula still calculating A3/B3. Wrap the actual calculation with IFERROR or an IF branch when the final display cell must avoid an error. [A1, A2]

• FALSE is not an indication that the source was numeric. If you enter valid text, ISERROR returns FALSE. If you need to check a type such as a number, consult Apple’s ISNUMBER or ISNUMBERORDATE functions instead; their results are distinct questions. [A1]
• Wrong error check: =ISERROR(A3) checks whether A3 itself is an error; it does not check the proposed division A3/B3. Test the full expression you mean to validate. [A1, M1]
• Unexpected TRUE: inspect the inner expression on its own in a temporary cell or use the Formula Editor’s error details, then fix the underlying zero divisor or invalid reference. [E1]
• Long, repeated formulas: prefer a single IFERROR when you only need a fallback. Repeated expressions make maintenance and diagnosis harder. [A2]
• Exact error classes and display codes: Apple’s ISERROR page confirms detection of an error in general. It does not enumerate every error message or cross-product error mapping, so this guide does not promise Excel-style codes. [A1]

Google Sheets officially documents ISERROR(value) and broad error detection. The high-level function name and purpose are shared, but Sheets’ specific error-code examples are not proof of which codes Numbers displays. In Excel and Sheets, test the source app independently if importing a workbook; application-specific error codes and coercion rules may differ. [G1, A1]

• Apple — ISERROR function — A1/A2, exact syntax, Boolean behaviour, comparison with IFERROR and example; accessed 2026-10-12 (current unversioned function URL).
• Apple — Formulas and Functions Help — V1, platform context and Functions Browser; accessed 2026-10-12.
• Apple — Refer to cells in formulas — R1, references and other tables; accessed 2026-10-12.
• Apple — Format a spreadsheet for another language — L1, region formats; accessed 2026-10-12.
• Google — ISERROR — G1, Sheets comparison only; accessed 2026-10-12.

This guide was checked against Apple’s English Formulas and Functions Help on 12 October 2026. The official function page is a Numbers Help 15.4 URL unless noted otherwise. Apple’s current Mac user guide identifies Numbers 15.4; the function’s first-ever release and behaviour in older Numbers versions have not been independently established. Apple also describes the Functions Browser in Numbers on Mac, iPhone, iPad, and iCloud.com; do not assume all historical versions are identical. [V1]

Numbers formulas operate inside tables, not against an undifferentiated worksheet grid. For the examples, create one table with the stated row/column dimensions; a plain reference such as B7 points into the formula’s table. To refer to a different table, Apple’s syntax uses Table 2::B7; for another sheet, it may be Sheet 2::Table 1::C5. In the Formula Editor, selecting the source cell is safer than typing a cross-table name manually. References inside a range use a colon, e.g. B2:D6. [R1]

The copyable formulas use English-language function names and comma separators as displayed in the cited English Apple help. Apple’s language/region settings affect number, currency, and date formatting; the exact argument separator and localized function spelling for every locale were not natively tested. If your Numbers Formula Editor presents different separators, use what it shows rather than copying punctuation blindly. For these reference-and-Boolean functions, changing the decimal locale does not change the intended row/column count or TRUE/FALSE logic. [L1]

Validation distinction: Numbers was not run. Outputs labelled expected below are either explicitly illustrated in Apple’s documentation or independently calculated from the example’s defined table coordinates/logic. No screenshot or application-observed result is claimed.

Source version nuance: Apple currently serves the ISERROR function page at an unversioned /web URL. It appears in the current Functions Help table of contents; do not infer a specific first-supported release from that URL.

Documentation and independent arithmetic reviewed. No native Apple Numbers execution or historical-version test was performed; exact error messages remain unverified.