How to Audit Estimates and Fair Values Under ISA 540

The client’s expected credit loss provision dropped 40% year on year. Revenue grew. The debtor book aged. And the ECL went down. When you asked the financial controller, the answer was “we updated the model.” No further explanation. No sensitivity analysis. No documentation of the assumptions that changed. ISA 540 exists because estimates are where management has the widest latitude to get the numbers wrong, intentionally or otherwise.

To audit accounting estimates and fair values under ISA 540 (Revised), the auditor must understand the entity’s process for making estimates (ISA 540.13), identify and assess the risks of material misstatement (ISA 540.16), design responses that address estimation uncertainty and the potential for management bias (ISA 540.17–18), and evaluate the reasonableness of the estimate and related disclosures against the applicable financial reporting framework.

Why estimates are the hardest area to get right

Every other audit assertion has a natural anchor. Cash ties to the bank confirmation. Revenue ties to invoices and delivery documentation. Fixed assets tie to purchase contracts and physical existence. Estimates don’t tie to anything external in the same way. They’re forward-looking judgments built on assumptions, and the range of reasonable outcomes can be wide enough that two competent accountants could produce materially different numbers from the same data.

ISA 540.2 acknowledges this directly: accounting estimates vary widely in their nature, the degree of estimation uncertainty, and the complexity of the methods used to make them. That variation means your audit approach can’t be uniform. A straightforward inventory provision based on ageing data requires different procedures than a fair value measurement of an unquoted equity investment using a discounted cash flow model. Both are estimates. One needs a recalculation check. The other might need a management’s expert, a sensitivity analysis, and an independent range estimate.

The revised ISA 540 (effective for periods beginning on or after 15 December 2019) restructured the standard around four inherent risk factors. Estimation uncertainty and complexity are the first two. Subjectivity is the third. The fourth is how these factors interact with each other on a specific estimate. Every estimate gets assessed against these factors, and your response scales accordingly. A low-complexity estimate with low uncertainty (a depreciation charge using a standard straight-line method) sits at one end. A high-complexity estimate with high uncertainty and high subjectivity (a Level 3 fair value measurement with unobservable inputs) sits at the other. ISA 540.16 requires you to identify where each estimate falls on that spectrum before designing procedures.

What ISA 540 (Revised) changed and why it matters for your file

Under the previous version of ISA 540, a more binary approach was acceptable: test management’s estimate, develop your own, or review subsequent events. The revised standard doesn’t remove those options (they appear in ISA 540.18), but it wraps them in a risk assessment framework that forces you to document why you chose the approach you chose.

What changed most in practice is the emphasis on the “stand back” evaluation. ISA 540.34 requires the auditor to evaluate, based on the audit procedures performed and evidence obtained, whether the accounting estimates and related disclosures are reasonable in the context of the applicable framework. Paragraph 35 then requires a separate assessment of whether indicators of possible management bias exist. These aren’t review points. They’re required procedures with their own documentation.

Another change that affects mid-tier files: ISA 540.14 made the retrospective review a planning procedure, not an afterthought. You compare prior-year estimates to actual outcomes (or to subsequent re-estimates) to understand the entity’s estimation process, to identify inherent risk factors, and to detect indicators of management bias. The comparison must be specific enough to be useful. Noting that “prior year provisions were materially in line with actuals” doesn’t satisfy ISA 540.14 if the individual estimates moved in opposite directions that happened to net off.

The three audit responses and how to choose between them

ISA 540.18 gives you the response options. Your choice depends on the nature of the estimate, the availability of data, and the level of estimation uncertainty.

Evidence from subsequent events (ISA 540.18(a))

This is the strongest form of evidence because it replaces the estimate with an actual outcome. If the client has a year-end provision for a legal claim and the case settles before you sign the audit report, the settlement amount is better evidence than any estimate. Use this response where subsequent events resolve the estimate entirely or narrow the range substantially. The limitation is timing: many estimates don’t resolve within the audit window. An expected credit loss provision won’t crystallise into actual defaults within two months of year-end.

Testing management’s process (ISA 540.18(b))

This is the most common response on mid-tier engagements. You test the method, the data, and the assumptions. ISA 540.18(b) breaks this into components: whether the method is appropriate under the framework, whether the data is complete and accurate, whether the significant assumptions are reasonable, and whether the calculations are mathematically correct. For a fair value estimate, “testing the method” means evaluating whether the valuation technique (market approach, income approach, cost approach under IFRS 13.61–66) is appropriate given the nature of the asset or liability and the availability of observable inputs.

Developing an auditor’s estimate or range (ISA 540.18(c))

You build your own estimate using different data, a different method, or different assumptions, then compare your result to management’s. This works well for estimates where the inputs are available but management’s judgment is questionable. For an expected credit loss provision, you might run the client’s debtor book through your own probability-of-default model (or a published model for the client’s industry) and compare the output to management’s provision. If your range is €180,000 to €240,000 and management’s provision is €195,000, the estimate sits within a reasonable range. If management’s provision is €85,000, you have a presumptive misstatement.

Developing your own estimate is more work than testing management’s process. But it produces the strongest evidence for estimates with high subjectivity because you’re not anchored to management’s assumptions. For fair value measurements, this may involve engaging an auditor’s expert under ISA 620 to produce an independent valuation.

How to run the retrospective review properly

ISA 540.14 requires a comparison of prior-period estimates to the actual outcomes (or the subsequent re-estimates made in the current period). Most files include this as a table: prior year estimate in one column, actual or current year re-estimate in the other, difference in the third. That format is correct. The analysis that accompanies it is where files fail.

The purpose of the retrospective review isn’t to confirm that the client’s estimates were “approximately right.” It serves four distinct functions under ISA 540.14: understanding the entity’s estimation process, identifying estimation uncertainty indicators, detecting possible management bias, and informing the current-year risk assessment. If your retrospective review note says “prior year estimates were within an acceptable range of actual outcomes” and nothing else, you’ve addressed none of these functions specifically.

The key: do this for each material estimate individually. Don’t net provisions against warranty claims against restructuring costs. An accurate total can hide directional bias in the components.

Identifying management bias in estimates

ISA 540.32 requires you to evaluate whether indicators of possible management bias exist. ISA 540.A129 lists the types of indicators you’re looking for. The critical ones for mid-tier engagements are directional consistency, anchoring behaviour, and selective use of assumptions.

Directional consistency

Directional consistency means the estimates all move in the same direction. If every judgmental estimate on the file sits at the optimistic end of the range (low provisions, high asset valuations, long useful lives, aggressive revenue recognition on estimates), that’s a bias indicator. No single estimate may be unreasonable on its own. The pattern is the problem.

Anchoring

Anchoring happens when management sets the current-year estimate equal to the prior year without updating for changed circumstances. If the client’s warranty provision has been exactly €120,000 for four consecutive years despite revenue growth of 30%, the provision hasn’t been re-estimated. It’s been copied. ISA 540.14 should catch this through the retrospective review, but only if you compare the provision to the underlying risk drivers (warranty claim rates, revenue volume) rather than just to the actual claims.

Selective use of assumptions

Selective use of assumptions is the subtlest indicator. The client uses conservative assumptions for some inputs and aggressive ones for others, always in the direction that produces a favourable result. A property developer might use conservative cost estimates (reducing profit recognition on percentage-of-completion contracts) while simultaneously using aggressive selling price assumptions (increasing the net realisable value of inventory). Both assumptions are individually within a defensible range. Together, they produce an NRV calculation that’s systematically overstated.

Worked example: Janssen Bouwgroep B.V.

Janssen Bouwgroep B.V. is a mid-sized Dutch construction company. Revenue for 2024: €85M. The balance sheet includes a warranty provision of €640,000, an expected credit loss provision of €195,000, and a percentage-of-completion revenue accrual on four active projects totalling €12.4M. Fair value measurement: one investment property carried at €3.8M under IAS 40, valued internally by management using the income capitalisation approach.

1. Retrospective review (ISA 540.14)

Compare each prior-year estimate to its outcome:

2. Risk assessment (ISA 540.16)

The investment property fair value has the highest inherent risk. It uses an internally generated valuation (no external appraiser), it relies on unobservable inputs (the capitalisation rate and projected rental income), and the retrospective review shows a history of overstatement. Assess this as a significant risk. The warranty provision has moderate estimation uncertainty (large variance from actual) but low complexity (simple actuarial-style calculation from historical claim rates). Assess this as a non-significant risk with moderate inherent risk factors.

3. Audit response for the investment property (ISA 540.18(c))

Develop an independent estimate. Obtain comparable rental yields for commercial property in the same municipality from Vastgoedmarkt or NVM commercial data. Management used a capitalisation rate of 5.8%. Published yields for comparable properties in the same area range from 6.2% to 7.1%. Using a mid-range rate of 6.5% against management’s projected net rental income of €228,000, the independent estimate is €228,000 / 6.5% = €3,508,000. Management’s carrying amount is €3.8M. The difference of €292,000 exceeds performance materiality (€170,000).

4. Stand-back evaluation (ISA 540.34–35)

Across all estimates: warranty was under-provided (favourable to profit), the investment property was overstated (favourable to profit and net assets), and the PoC accrual was over-recognised (favourable to revenue). Only the ECL provision moved in the unfavourable direction, by a small amount. This pattern is consistent with management bias toward overstating profit. Document the finding and raise it with those charged with governance under ISA 260.

Conclusion. The file shows a quantified misstatement on the investment property (€292,000), a directional bias pattern across four estimates, and a specific retrospective review that identified two consecutive years of warranty under-provision. The reviewer sees the individual estimate assessments, the independent valuation with market data, and a documented bias evaluation that connects the findings across estimates.

Your engagement checklist

1. Run the retrospective review for every material estimate at planning. Compare prior-year estimate to actual outcome individually (not netted). Document the direction and magnitude of each difference (ISA 540.14).
2. Assess inherent risk factors (estimation uncertainty, complexity, subjectivity) for each material estimate. Record the assessment in the risk assessment working paper before designing procedures (ISA 540.16).
3. For each estimate assessed as a significant risk, choose a response under ISA 540.18 and document why that response is appropriate for the specific risk factors identified.
4. Test the data inputs to management’s estimate for completeness and accuracy. For an ECL provision, that means testing the debtor ageing report to the general ledger, not just accepting management’s extract (ISA 540.18(b)).
5. Perform the stand-back evaluation after completing all estimate procedures. Evaluate whether the estimates individually and in aggregate indicate management bias. Document the conclusion (ISA 540.34–35).
6. For fair value measurements using unobservable inputs (Level 3 under IFRS 13), consider whether an auditor’s expert is needed to develop an independent estimate or evaluate management’s valuation technique.

Common mistakes regulators flag

• The FRC’s 2022–23 Audit Quality Inspection Report found that audit teams routinely failed to assess estimation uncertainty, complexity, and subjectivity as separate inherent risk factors. Many files combined them into a single assessment, which prevented the team from designing responses targeted at the specific risk driver. ISA 540.16 requires separate consideration.
• The AFM has flagged insufficient retrospective reviews across multiple inspection cycles. The most common deficiency: the review exists but contains no analysis. A table comparing prior-year to actual is not the review. The analysis of what the comparison means for estimation quality, bias indicators, and current-year risk assessment is the review (ISA 540.14).

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