Auditing
Tests of Controls vs Tests of Details: When and Why Auditors Use Them
By SimplyCPA · 11 October 2026
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- Test of controls: Evaluates whether a control operated effectively. Its output is a deviation rate, not a dollar amount.
- Test of details: A substantive procedure that tests individual transactions or balances for monetary misstatement.
- Significant risks: Controls relied on must be tested in the current period. If the response is substantive only, it must include tests of details.
- Interim testing: Both can be done before year-end, but the auditor must cover the remaining period with further procedures (a roll-forward).
- Choosing: Reliable controls let the auditor reduce the nature, timing and extent of tests of details — but never eliminate substantive procedures for material items.
The core difference
| Test of controls | Test of details | |
|---|---|---|
| Question | Did the control operate effectively throughout the period? | Is this transaction or balance materially misstated? |
| Measured as | Deviation rate | Dollar misstatement |
| Typical techniques | Inspection of evidence of review, observation, inquiry combined with other procedures, reperformance | Vouching, tracing, confirmation, recalculation, physical inspection, cutoff tests |
| Sampling approach | Attribute sampling | Variables or monetary-unit sampling |
| Required? | When relying on controls, or when substantive procedures alone can't provide enough evidence | Substantive procedures are always required for material items; tests of details specifically for significant risks addressed only substantively |
Example: the revenue cycle
- Test of control: select 40 sales orders and inspect each for evidence that credit was approved before shipment. Two exceptions = a 5% deviation rate, compared with the tolerable rate.
- Test of details: select a sample of recorded sales and vouch each to the shipping document and customer order (occurrence), recalculate the invoice (accuracy), and check the shipment date against the recording date (cutoff).
Significant risks
For a significant risk, AU-C 330 requires that:
- if the auditor plans to rely on controls over the risk, those controls are tested in the current period — no reliance on prior-year evidence; and
- if the approach consists only of substantive procedures, they must include tests of details — substantive analytical procedures alone aren't enough.
Interim testing and roll-forward
- Controls tested at an interim date: obtain evidence about significant changes after the interim date and decide what additional evidence is needed for the remaining period, considering the significance of the risk and the length of the period.
- Substantive tests at an interim date: cover the remaining period with substantive procedures, or substantive procedures combined with tests of controls, so there's a reasonable basis for extending the conclusions to year-end.
- Where the risk of material misstatement is high, the auditor usually performs tests of details at or near year-end.
Dual-purpose tests
The same sample can serve both purposes — for instance, checking each invoice for approval (control) and for correct pricing (substantive). The auditor designs it with both objectives in mind and evaluates the control deviations and the dollar misstatements separately.
Exam pattern: If a question asks how the auditor responds to a control that failed, the answer usually involves increasing the extent of tests of details, moving them closer to year-end, or switching to more reliable evidence — not "performing more tests of controls".
Read alongside internal controls vs substantive procedures and audit sampling.