Advanced Audit and Assurance (International) · Evidence and testing considerations

Auditing Accounting Estimates and Fair Values (ISA 540) for ACCA AAA

Updated 11 October 2026 · Fact-checked

ISA 540 (Revised) deals with auditing accounting estimates, including fair values. You assess estimation uncertainty, complexity and subjectivity, then respond by testing events to date, testing management's method, or building your own point estimate or range. You evaluate bias and disclosures, and conclude on reasonableness.

Understand Auditing Accounting Estimates and Fair Values (ISA 540)

An accounting estimate is a monetary amount that cannot be observed directly, so management has to measure it with judgement. Examples are expected credit losses, inventory write-downs, provisions, impairment of goodwill, deferred tax assets, useful lives and fair values of unquoted investments.

The risk is that the estimate is wrong, and that the error is deliberate. ISA 540 (Revised) asks you to assess three inherent risk factors: estimation uncertainty (how imprecise the measurement is), complexity (how difficult the method, data or assumptions are) and subjectivity (how much judgement management applies). It also asks you to consider other factors such as susceptibility to management bias or fraud. The higher these are, the higher the assessed risk of material misstatement. Where inherent risk is assessed as high, it may be a significant risk.

Your risk assessment starts with understanding how management makes the estimate: the applicable financial reporting framework (for example IFRS 9, IAS 36, IAS 37 or IFRS 13), the method and model used, the assumptions, the data, whether management uses an expert, and the controls over the process. You also review the outcome of prior-period estimates. Differences between past estimates and actual results can reveal bias or weak processes.

Your response follows from the risks. ISA 540 (Revised) gives you approaches, which you can combine: obtain evidence from events occurring up to the date of the auditor's report; test how management made the estimate (method, assumptions, data); or develop an auditor's point estimate or range. Using an auditor's expert (ISA 620) is common for complex valuations.

Finally, you stand back. You evaluate whether the estimates and related disclosures are reasonable under the framework, whether there are indicators of management bias, and whether the evidence is sufficient and appropriate. You obtain written representations on the estimates and communicate significant matters to those charged with governance. Indicators of bias may be a control deficiency and affect the audit opinion if material.

Key rules to remember

Inherent risk factors (ISA 540 Revised): Estimation uncertainty + Complexity + Subjectivity (+ other bias or fraud susceptibility); Use these as labels when assessing risk. Higher levels mean higher inherent risk and more persuasive evidence needed.
Responses to assessed risk: Subsequent events | Test management's method, assumptions and data | Auditor's point estimate or range; You can use one or more. Name the one you choose and say why it suits the scenario.
Auditor's range: If management's point estimate lies outside your range, misstatement = difference between management's estimate and the nearest point of your range; If it lies within a range based on reasonable assumptions, evidence supports it. Do not treat this as a rigid rule, use judgement.
Fair value hierarchy (IFRS 13): Level 1: quoted prices | Level 2: observable inputs | Level 3: unobservable inputs; Level 3 measurements carry the highest estimation uncertainty and subjectivity, so expect a significant risk.
Bias review: Compare prior-year estimates with actual outcomes, and review judgements for a consistent direction; Bias is a one-directional pattern, such as always optimistic. ISA 540 treats it as a matter to evaluate, not automatically as fraud.

How to solve Auditing Accounting Estimates and Fair Values (ISA 540) questions

Use this order for any question on estimates, whatever the balance (provision, impairment, receivables or fair value).

1Identify the estimate and the framework that governs it, for example IAS 36 for impairment or IFRS 9 for credit losses.
2Assess the inherent risk using uncertainty, complexity and subjectivity, and link each to facts in the scenario. Say whether it is a significant risk.
3Identify bias indicators: management incentives, covenants, bonuses, changes in method, optimistic assumptions, and prior-year estimates that proved wrong.
4Select the audit response approach (events to date, test management's process, or own estimate or range) and justify the choice.
5List specific procedures: inspect data, recalculate, compare assumptions with market or board-approved budgets, check subsequent events, and consider an expert under ISA 620.
6Evaluate: is the estimate reasonable, are disclosures adequate, and is there bias? Quantify any misstatement and consider the effect on the opinion.
7Add completion actions: written representations, communication to those charged with governance, and the professional scepticism you applied.

Quickest way: Risk, bias, procedures, conclusion

When to use it: When time is short and the requirement asks for audit procedures or risks on one estimate.

Write one line naming the estimate and the standard that measures it.
Give two risk points: why it is uncertain, complex or subjective, plus any bias motive in the scenario.
Give 4 to 6 procedures, each tied to a scenario fact. Include one on subsequent events, one on assumptions and one on data.
Close with one line on evaluating reasonableness, disclosures and bias, and on the expert or representations if relevant.

Common mistakes in Auditing Accounting Estimates and Fair Values (ISA 540)

Listing generic audit procedures such as inspect and recalculate with no link to the scenario.
Students memorise lists and skip the application that earns marks.
Fix: Tie every procedure to a named fact, such as the discount rate, the customer or the product line in the question.
Treating all management bias as fraud.
Bias and fraud sound similar and students overstate.
Fix: Say bias is an indicator you evaluate. It may be unintentional. If intentional, consider fraud risk under ISA 240.
Ignoring prior-year estimates.
Students focus on the current-year figure only.
Fix: Include a retrospective review comparing last year's estimate with the actual outcome as evidence of reliability and bias.
Accepting management's expert or valuation report without challenge.
A professional report feels reliable.
Fix: Assess the expert's competence, capabilities and objectivity, and test the data and assumptions used. Consider your own expert under ISA 620.
Forgetting disclosures.
Students think of estimates as only a number.
Fix: Evaluate whether disclosures of assumptions and estimation uncertainty meet the framework, for example sensitivity disclosures for Level 3 fair values.
Confusing the three response approaches, or applying them rigidly.
Students recall the list but not when each fits.
Fix: Use subsequent events when events give evidence quickly, test management's process for models, and your own range when management's method is questionable.

Worked examples

Example 1

Danvil Co, an audit client, holds an unquoted equity investment valued at $4.2 million using a discounted cash flow model prepared by management. Growth assumptions are above the industry average and the finance director's bonus depends on profit. Explain the audit risks and the procedures you would perform. (10 marks style, shortened)

Show the solution

Estimate and framework: fair value of an unquoted investment under IFRS 13 using inputs that are unobservable, so Level 3.
Risk: high estimation uncertainty because cash flows depend on future events. High complexity because of the DCF model. High subjectivity in growth and discount rates. This is likely a significant risk.
Bias: the bonus linked to profit gives a motive to overstate fair value gains, and growth above industry average points to optimism.
Procedure 1: understand management's process and controls, and test the integrity of the model through recalculation.
Procedure 2: compare growth assumptions with the investee's approved budgets, past actual results and industry data. Challenge differences.
Procedure 3: assess the discount rate with an auditor's valuation expert under ISA 620, including whether it reflects the risk of the investee.
Procedure 4: perform a retrospective review of last year's valuation against actual results, and review post year-end events and trading.
Procedure 5: evaluate sensitivity, develop an auditor's range if needed, and check IFRS 13 disclosures for Level 3 inputs.
Conclude on reasonableness, evaluate bias, and obtain written representations.

Answer: The investment is a significant risk because it is a Level 3 fair value with high uncertainty, complexity, subjectivity and a bias motive. Respond by testing the model, challenging assumptions with independent evidence and an expert, reviewing prior outcomes and subsequent events, and evaluating disclosures and bias.

Example 2

Brantley Co has receivables of $8.0 million. Management has set the credit loss allowance at $0.2 million, down from $0.5 million last year, though one major customer owing $1.5 million has been paying 60 days late and a retrospective review shows last year's allowance was $0.1 million higher than actual write-offs. Identify the concerns and the procedures.

Show the solution

Calculate the movement: the allowance fell from $0.5 million to $0.2 million, a reduction of $0.3 million, even though credit risk appears to have risen.
Concern 1: the reduction is inconsistent with late payment by a customer owing $1.5 million, which is 18.75% of receivables ($1.5m ÷ $8.0m). It suggests understatement and possible bias to raise profit.
Concern 2: the retrospective review shows last year's allowance was too high by $0.1 million. That suggests some past prudence, so the change may be a method change that needs to be understood and justified rather than assumed biased.
Procedure 1: obtain management's expected credit loss model under IFRS 9 and test the inputs, such as ageing data, historic loss rates and forward-looking adjustments.
Procedure 2: examine cash received after year end from the major customer and review correspondence and credit status.
Procedure 3: recompute the allowance using the ageing and loss rates, and compare with management's figure to form a range.
Procedure 4: ask why the method changed and check consistency with IFRS 9 and disclosures.
Conclude, and quantify any shortfall against the range and compare with materiality.

Answer: The allowance fall of $0.3 million looks unsupported given the late-paying customer who represents 18.75% of receivables, though the prior-year overprovision means you must test the method before alleging bias. Test the ECL model, subsequent receipts, and your own recalculation, then evaluate any shortfall against materiality.

Exam tips

Always say which of the three response approaches you will use and why. This shows the structure of ISA 540 (Revised).
Use the scenario's incentives (bonuses, covenants, targets) to explain bias. Generic bias statements score poorly.
Include professional skills: be sceptical of management, communicate clearly to those charged with governance, and show commercial awareness.
For fair values, state the IFRS 13 level. Level 3 means significant risk, an expert and sensitivity disclosures.
If the question gives numbers, compute the difference or percentage and compare with materiality before concluding.

Practice questions from Evidence and testing considerations

Auditing Accounting Estimates and Fair Values (ISA 540) in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

CA FinalSA 540: Auditing Accounting Estimates and Related Disclosures

Auditing Accounting Estimates and Fair Values (ISA 540): frequently asked questions

What does ISA 540 (Revised) require for risk assessment?

You must understand the entity, the framework requirements, and how management makes the estimate. You then assess inherent risk using estimation uncertainty, complexity, subjectivity and susceptibility to bias, and decide whether there is a significant risk.

How do you identify management bias in estimates?

Look for a consistent direction in judgements, changes in method or assumptions without clear reason, optimistic inputs, and prior-year estimates that differed from actual outcomes. Consider management's incentives such as bonuses and covenants. Bias is evaluated and may indicate fraud risk.

How is auditing fair values different from other estimates?

Fair values follow IFRS 13 and the input hierarchy. Level 1 inputs can be agreed to market prices, while Level 3 inputs need heavy challenge, often with an expert. The extra step is checking the level and the related disclosures.

Can I use an expert to audit an estimate?

Yes. ISA 620 applies when you use an auditor's expert. You assess the expert's competence, capabilities and objectivity, agree the scope of work and evaluate whether their work is adequate for your purpose. You remain responsible for the audit opinion.