How to Audit Accounting Policy Changes, Estimate Changes, and Prior Period Errors Under IAS 8

The classification problem that drives most IAS 8 findings

The hardest part of IAS 8 isn’t the accounting treatment. Retrospective application and prospective application are both well-defined mechanical processes. The hard part is deciding which one applies, because that depends entirely on whether the change is a policy change, an estimate change, or an error correction. Get the classification wrong and every subsequent step (the accounting treatment, the comparatives, the disclosure note) is also wrong.

Before the 2021 amendment to IAS 8 (effective for periods beginning on or after 1 January 2023), the distinction between a policy change and an estimate change was genuinely ambiguous in some cases. The IASB acknowledged this. The amendment added a definition of accounting estimates to IAS 8.5: “Accounting estimates are monetary amounts in financial statements that are subject to measurement uncertainty.” This definition didn’t change the classification of most items, but it clarified the boundary. A depreciation method is a technique for estimating the pattern of consumption of future economic benefits. It isn’t a policy. IAS 8.32A (added by the amendment) confirms that a change in a measurement technique is a change in an accounting estimate unless it results from correcting an error.

If your engagement has any change in how the client measures a balance sheet item, the first question on your working paper should be: is this a change in accounting policy or a change in accounting estimate under IAS 8.32? The answer determines everything else.

What IAS 8 requires: the three-way split

IAS 8 deals with three distinct situations. Each has its own recognition rule, its own measurement approach, and its own disclosure requirement.

A change in accounting policy occurs when the entity changes the principles, bases, conventions, rules, or practices it applies in preparing financial statements (IAS 8.5). IAS 8.14 permits voluntary policy changes only when the new policy results in reliable and more relevant information. Mandatory policy changes (required by a new or amended IFRS) follow the transitional provisions in that standard; voluntary changes require retrospective application under IAS 8.22 as if the new policy had always been applied.

A change in accounting estimate occurs when the entity revises an estimate as a result of new information or new developments (IAS 8.34). The 2021 amendment clarified that this includes changes in measurement techniques and changes in inputs to those techniques, unless the change corrects a prior period error. Prospective application only. IAS 8.36 is explicit: the change affects the current period and future periods. No restatement of comparatives.

A prior period error is an omission or misstatement in one or more prior period financial statements arising from a failure to use, or the misuse of, reliable information that was available and could reasonably be expected to have been obtained (IAS 8.5). IAS 8.42 requires retrospective restatement: correct the prior period amounts and restate comparatives as if the error had never occurred.

The accounting treatments are mirror images of each other. Policy changes go backward (retrospective). Estimate changes go forward (prospective). Errors also go backward (retrospective restatement). Getting the direction wrong is the misstatement.

How to test whether a change is a policy change or an estimate change

The classification test follows IAS 8.32 to IAS 8.35 and the 2021 amendment’s additions.

Ask two questions. First: has the entity changed the principle or basis it uses to recognise, measure, or present a class of transactions or balances? If yes, it’s a policy change. A switch from FIFO to weighted-average cost for inventory valuation changes the measurement basis. That’s IAS 8.14.

Second: has the entity changed the inputs, assumptions, or techniques it uses to arrive at a monetary amount that was already subject to estimation? If yes, it’s an estimate change. Revising the expected credit loss rate on trade receivables from 2% to 3.5% based on updated customer payment data changes the inputs to an estimate. Switching the depreciation method from straight-line to reducing balance changes the technique for estimating the consumption pattern. Both are estimate changes under IAS 8.32.

When both questions produce a “yes” answer, IAS 8.35 applies: treat the entire change as a change in accounting estimate. Prospective treatment. This tiebreaker is rare but important to document.

Here’s the working paper structure. For each change identified during the engagement, document four things: what changed, why it changed, which IAS 8 paragraph governs the classification, and what accounting treatment follows. That four-column table is your evidence that the classification was tested, not assumed.

A common grey area: a client switches its IFRS 9 expected credit loss model from a provision matrix based on ageing to a probability-weighted model based on forward-looking macroeconomic factors. The measurement basis hasn’t changed (IFRS 9 still governs ECL measurement). The technique has changed. IAS 8.32A treats this as an estimate change. Prospective application. No restatement.

Auditing retrospective application under IAS 8.22

When a client makes a voluntary policy change, IAS 8.22 requires retrospective application. The entity must adjust the opening balance of each affected component of equity for the earliest period presented, and restate the other comparative amounts as if the new policy had always been applied.

Your audit work covers four areas. First, verify that the policy change qualifies under IAS 8.14: does the new policy provide more relevant or reliable information? The entity should be able to articulate why. “Our peers use this method” is not sufficient justification under IAS 8.14(b). Second, test the restatement arithmetic. The entity needs to calculate what each prior period balance would have been under the new policy. For a change in revenue recognition policy, that means re-running the revenue calculation for each restated period. Third, check the IAS 8.28 disclosures: the nature of the change, the reasons, the amount of adjustment for each line item affected, and the amount of adjustment to basic and diluted EPS. Fourth, verify that the opening balance of retained earnings (or the relevant equity component) for the earliest comparative period carries the cumulative effect of the change.

IAS 8.23 to IAS 8.27 provide the impracticability exception. If the entity cannot determine the period-specific or cumulative effect of the change, it applies the new policy from the earliest date practicable. “Impracticable” has a high bar under IAS 8.5: it means the entity cannot apply the requirement after making every reasonable effort to do so. Time pressure or cost alone do not qualify. Document the entity’s assessment of impracticability and whether you concur.

If the entity is applying a new IFRS for the first time, the transitional provisions in that specific standard override IAS 8.22. IFRS 16’s transition rules, for example, allowed a modified retrospective approach that IAS 8 alone wouldn’t permit. Check the specific standard before defaulting to IAS 8.

One practical trap: a client makes a voluntary policy change and also discovers a prior period error in the same reporting period. Both require retrospective restatement of comparatives, but the disclosures are separate. IAS 8.28 governs the policy change disclosure. IAS 8.49 governs the error correction disclosure. Combining them into a single note obscures which adjustments are policy-driven and which are error-driven, and a reviewer will ask for the split. Prepare separate disclosure checklists for each.

Auditing prior period errors under IAS 8.42

Prior period errors are different from policy changes in one important respect: an error means the prior period financial statements were wrong when issued. IAS 8.41 defines the information test. The information must have been available when those financial statements were authorised for issue and could reasonably have been expected to have been obtained.

This distinction matters on the engagement. If a client discovers that it underaccrued a warranty provision by €600K in the prior year because it used a 1% claims rate when its own internal data showed 2.8%, that’s an error under IAS 8.41. The data existed. It was available. It should have been used. But if the client used 1% because that was the best estimate available at the time, and subsequent experience revealed 2.8%, that’s new information. The revision is an estimate change (IAS 8.34), not an error correction.

The timing test is what separates errors from estimates in practice. Ask the client: when did you first have access to the information that changes this number? If the answer is “before we signed the prior year financial statements,” you’re looking at an error. If the answer is “this year, when new data became available,” you’re looking at an estimate revision. Document the answer and the evidence supporting it. This single question resolves the classification in most cases.

IAS 8.42 requires the entity to correct the error by retrospective restatement, restating comparative amounts for the prior period in which the error occurred. If the error occurred before the earliest period presented, the entity restates the opening balances of assets, liabilities, and equity for the earliest period presented (IAS 8.43).

For your audit working paper, test four things. First, confirm the error meets the IAS 8.41 definition: was the information available, and was it reasonable to expect the entity to have used it? Second, trace the restatement amounts to re-performed calculations. Third, verify the IAS 8.49 disclosures: the nature of the error, the amount of correction for each financial statement line item, and the amount of correction to basic and diluted EPS. Fourth, check that the auditor’s report on the prior period financial statements (if applicable) is referenced in any reissue or communication under ISA 560.14.

Review the ISA 520 Analytical Review Calculator output for unusual movements in provisions, accruals, and estimates. A large prior-year adjustment that appears as a “change in estimate” might actually be an error correction that requires restatement. The analytical review flags the movement; IAS 8 tells you what to do with it.

Worked example: De Groot Bouw B.V.

Client profile: De Groot Bouw B.V. is a Dutch construction company with €38M revenue, reporting under IFRS. During the current year audit, the team identified two IAS 8 events: a change in inventory valuation method and a prior period error in revenue recognition.

1. Classify the inventory method change

De Groot switched its inventory valuation from FIFO to weighted-average cost, effective 1 January of the current year. The financial controller argues it better reflects the physical flow of materials in the construction business, where materials from different purchases are mixed on-site.

This is a change in accounting policy under IAS 8.5. The entity changed the measurement basis for inventories from one permitted method (IAS 2.25) to another. IAS 8.14(b) requires the entity to demonstrate that the new policy provides more relevant information. De Groot’s rationale (physical flow matching) is supportable.

The prior year comparatives need restatement under IAS 8.22. De Groot recalculated prior year closing inventory under weighted-average cost: €4.3M (compared to €4.7M under FIFO). That €400K difference reduces prior year cost of sales, increasing prior year profit by €400K before tax. A corresponding increase in the prior year deferred tax liability of €100K follows (25% Dutch corporate tax rate). Net effect on opening retained earnings for the current year: €300K.

2. Classify and correct the revenue recognition error

During testing of construction contracts, the team found that De Groot recognised €520K of revenue in the prior year for a project where the performance obligation under IFRS 15.35 had not been satisfied. The project’s completion percentage was overstated because the entity used outdated cost forecasts that its own project manager had revised downward three months before year-end. The revised forecasts were available in the project management system.

This is a prior period error under IAS 8.41. The information (the revised cost forecast) was available when the prior year financial statements were authorised for issue. De Groot should have used it.

IAS 8.42 requires retrospective restatement. The prior year revenue decreases by €520K. Contract assets decrease by €520K. The deferred tax asset increases by €130K. Opening retained earnings for the current year decreases by €390K. The revenue is recognised in the current year as the performance obligation is satisfied.

3. Document the combined effect on comparatives

The two IAS 8 events affect the same comparative period. De Groot’s restated comparative income statement shows two adjustments: a €400K increase in profit (from the inventory policy change) and a €520K decrease in revenue (from the error correction). The net effect on prior year profit before tax is a €120K decrease. The restated opening retained earnings for the current year carry the combined adjustment of €90K (€300K from inventory less €390K from revenue error, net of tax).

Practical checklist for your next engagement

1. At the start of fieldwork, ask the client whether any accounting policies changed during the year and whether any prior period errors were discovered. Get this on record before you find them yourself.
2. For every change identified, apply the IAS 8.32 classification test: did the entity change the measurement basis (policy change) or the inputs and techniques used to estimate a monetary amount (estimate change)? Document the answer with the specific IAS 8 paragraph.
3. For policy changes: verify the IAS 8.14 justification, test the restatement arithmetic against underlying records, and complete the IAS 8.28 disclosure checklist.
4. For estimate changes: confirm that the change is applied prospectively from the current period (IAS 8.36). Check the IAS 8.39 disclosures for the nature and amount of the change. If the amount can’t be estimated, confirm the entity discloses that fact (IAS 8.40).
5. For prior period errors: test the IAS 8.41 definition (was the information available at the time?), verify the restatement, and complete the IAS 8.49 disclosure checklist.
6. Cross-check all IAS 8 adjustments against the statement of changes in equity. The restated opening equity balances must reflect the cumulative effect of policy changes and error corrections. Reconciliation failures surface here.

Common mistakes

• Classifying depreciation method changes as policy changes: IAS 8.32 (and IAS 8.32A after the 2021 amendment) is explicit: depreciation method is an estimation technique. Prospective treatment only. The PCAOB’s 2023 staff inspection brief flagged this specific misclassification in two reviewed engagements.
• Accepting “change in estimate” without testing the IAS 8.41 definition: If the entity had the data at the time and failed to use it, it’s an error. The AFM’s 2023 inspection cycle noted that audit files frequently lacked documentation of the policy-versus-estimate-versus-error classification test.
• Omitting the EPS impact from disclosures: Both IAS 8.28 and IAS 8.49 require disclosure of the adjustment to basic and diluted earnings per share. Clients omit it because it requires recalculation. Auditors miss it because they check the narrative disclosure but not the numerical requirements.

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Further reading and source references

• IAS 8, Accounting Policies, Changes in Accounting Estimates and Errors: the source standard governing the three-way classification and its accounting treatment.
• ISA 710, Comparative Information: the audit standard relevant to the engagement partner’s assessment of restated comparatives.
• ISA 560, Subsequent Events: relevant to the auditor’s responsibilities when prior period errors are discovered after the auditor’s report has been issued.
• IAS 2, Inventories: the standard governing cost formula choices (FIFO, weighted average) that commonly trigger IAS 8 policy change assessments.