Retrospective Review of Prior-Year Estimates: AU-C 540, AU-C 240 and PCAOB AS 2401

Every audit file with estimates has a retrospective review line, and in many files it is a single sentence saying prior-year estimates were reviewed without exception. The standards ask for more: a comparison of what management estimated to what happened, and a conclusion about what the pattern says about this year's estimates. This post sets out the AICPA and PCAOB requirements, a worked comparison, and the documentation behind a real conclusion.

What does AU-C 540 require?

Paragraph .13 of AU-C 540, effective for audits of periods ending on or after December 15, 2023, requires the auditor to review the outcome of previous accounting estimates or, when applicable, their subsequent re-estimation, to help identify and assess the risks of material misstatement in the current period. The nature and extent of the review depend on the characteristics of the estimates. The review is "not intended to call into question judgments about previous-period accounting estimates that were appropriate based on the information available at the time they were made."

Paragraph .A55 lists what the review can tell the auditor: the effectiveness of management's previous estimation process, reasons for changes that may need disclosure, the complexity, subjectivity or uncertainty in the estimates, and susceptibility to or indicators of management bias. Paragraph .A56 says the review may cover the prior year or several periods, or shorter periods such as quarterly, and a multi-period review fits estimates that resolve slowly. Paragraph .A58 scales the work: higher inherent risk calls for a more detailed review, while for routine recurring estimates analytical procedures may be enough.

What does the fraud standard add?

AU-C 240, paragraph .32b, requires the auditor to review accounting estimates for bias and, under .32b(ii), perform a retrospective review of management judgments and assumptions related to significant accounting estimates in the prior year's financial statements. Estimates selected "should include those that are based on highly sensitive assumptions or are otherwise significantly affected by judgments made by management." Paragraph .A57 of AU-C 540 notes the two reviews can be performed together. The purpose in AU-C 240 (.A52) is to determine whether there is an indication of possible bias by management. See fraud risk assessment.

What is the PCAOB requirement?

AS 2401.64 requires a retrospective review of accounting estimates in significant accounts and disclosures by comparing the prior year's estimates to actual results, if any, to determine whether management's judgments and assumptions indicate possible bias. The estimates selected should be those with an assessed fraud risk. AS 2401.65 requires the auditor, on identifying possible bias, to evaluate whether the circumstances represent a risk of material misstatement due to fraud. AS 2810.24 to .27 covers assessing bias and its effect on the financial statements. For how this fits with the AS 2501 approaches, see AS 2501 estimates and fair value testing approaches.

How do you run it?

1. List the significant estimates from the prior-year file: reserves, accruals, fair values, useful lives, impairment inputs, revenue estimates.
2. Gather the outcome. For each, get the actual result: the credit memos issued, the warranty claims paid, the receivables collected or written off, the litigation settlement, the cash flows achieved.
3. Compute the difference in dollars, percent and direction.
4. Look at the pattern. One miss is noise. A consistent direction across unrelated estimates is the indicator.
5. Ask why. Differences driven by events after the estimate date are expected. Differences caused by information that was available when the statements were finalized point at the process (A60).
6. Carry the result forward into the current-year risk assessment and the work on this year's estimates.

Worked comparison

A distributor's prior-year reserves, compared to outcomes known by this year's fieldwork:

Four of five estimates were too high, each by 13% to 20%, and the net overstatement is $83,750, or 9.3% of a prior-year pretax income of $900,000 in this illustration. The one under-accrual is the litigation matter, where the outcome was a negotiated settlement.

What the auditor does with it:

• Raise the inherent risk of the same estimates this year and plan more persuasive evidence (AU-C 540.A60).
• Ask management to explain the common driver. If every reserve was set conservatively, that is a policy, and a policy of cushion reserves is an indicator of possible management bias under AU-C 540.32 even when each estimate is individually reasonable.
• Test the current-year releases. If last year's excess reserves are being reversed into income this year, the reversal is a source of the current-year earnings.
• Evaluate whether circumstances create a fraud risk (AU-C 240.32b(i), AS 2401.65), for example a bonus or covenant tied to earnings.
• Evaluate in aggregate. Under AS 2501.31 bias is assessed individually and in aggregate, including the cumulative effect of changes in estimates.

When does a difference become a misstatement?

AU-C 540.A60 says a difference between the outcome and the amount recognized "does not necessarily represent a misstatement of the previous period's financial statements." It may be one if it arises from information that was available when the statements were finalized or could reasonably have been obtained. In the example, a rise in customer returns after year-end caused by a product recall would not be a misstatement; a 20% allowance overage in a year with stable collections history suggests the opposite. Where an estimate is a fair value, A59 notes the review may focus on understanding the outcomes of assumptions and the effectiveness of the prior process rather than market movements.

Documentation

AU-C 540.38 requires documentation of indicators of possible management bias and the auditor's evaluation of the implications for the audit. Put these in the file:

• the list of estimates selected and why, tied to risk;
• the source of each outcome;
• the difference computation;
• the pattern conclusion and the management explanation;
• the effect on the current-year risk assessment and on audit procedures.

See point estimate, range and management bias for evaluating the current-year position.

Sources

• AICPA, AU-C Section 540, Auditing Accounting Estimates and Related Disclosures, paragraphs .13, .32, .38 and application material .A55 to .A60: https://www.aicpa-cima.com/resources/landing/aicpa-professional-standards
• AICPA, AU-C Section 240, Consideration of Fraud in a Financial Statement Audit, paragraph .32b and application material .A52 to .A53: https://www.aicpa-cima.com/resources/landing/aicpa-professional-standards
• PCAOB, AS 2401, Consideration of Fraud in a Financial Statement Audit, paragraphs .64 and .65: https://pcaobus.org/oversight/standards/auditing-standards/details/AS2401
• PCAOB, AS 2501, Auditing Accounting Estimates, Including Fair Value Measurements, paragraph .31: https://pcaobus.org/oversight/standards/auditing-standards/details/AS2501

CORAA prepares ready-to-review audit files for US CPA firms from client books; you review and sign. See /us.

AU-C references are to AICPA Professional Standards, paraphrased here; read the standard itself before relying on a requirement. This page is guidance, not professional advice. Report an error