Accounting Policies, Estimates & Prior Period Errors
Why a company revising its guess about how long a machine will last gets treated completely differently, in the accounts, from a company discovering it made an outright mistake in last year's numbers — even though both change a reported figure.
In plain English
Imagine three different situations. First: a company genuinely realises, based on new information, that a machine it assumed would last 10 years will now more likely last only 7 — a routine, forward-looking update to a judgement call. Second: a company decides to switch how it values inventory, from Weighted Average to FIFO, because it believes FIFO now gives a more relevant picture — a deliberate change in accounting POLICY. Third: an accountant discovers that last year's revenue figure was simply calculated wrong, due to a genuine arithmetic or data mistake — an outright ERROR. All three change a reported number, but accounting treats each one completely differently, and knowing which is which matters enormously for correctly interpreting a company's numbers.
Words you'll need first
A routine adjustment to a previous judgement call, caused by new information or new developments, NOT by a mistake — like revising an asset's useful life, a bad debt provision, or a warranty cost estimate. These are applied PROSPECTIVELY: only current and future periods are affected, and prior years' reported figures are never restated, since the earlier estimate was a genuinely reasonable judgement at the time it was made.
A genuine mistake in previously issued financial statements — arising from mathematical errors, misapplication of accounting policies, oversights, or misinterpretation of facts that existed at the time — as opposed to a reasonable judgement that simply turned out differently than expected. Material prior period errors must be corrected RETROSPECTIVELY: the comparative figures for the affected prior periods are restated as if the error had never been made.
Three different situations, three different fixes
Change in Estimate — fix going forward only
A machine's revised useful life, an updated bad debt estimate — these are corrected PROSPECTIVELY. This year's and future years' depreciation or provisions change; prior years' already-reported numbers stay exactly as they were.
Prior Period Error — restate the past
A genuine mistake — a formula error, a missed transaction, a misapplied rule — is corrected RETROSPECTIVELY. The comparative figures for the affected prior period(s) are restated in the current financial statements, as if the error had never happened.
A worked example, with numbers
| Item | Type | Accounting treatment |
|---|---|---|
| ₹50 crore prior-year revenue overstatement | Prior Period Error | Restate last year's comparative revenue down by ₹50 crore; opening retained earnings corrected |
| Machine useful life revised from 10 to 7 years | Change in Estimate | Apply the new, shorter life to remaining depreciation from THIS YEAR forward only |
| Net effect on prior-year published figures | — | Only the error triggers restatement; the estimate change does not |
- The ₹50 crore revenue error requires the company to go back and correct last year's comparative figures in this year's financial statements — anyone comparing this year's results to the restated prior year gets an accurate, apples-to-apples trend.
- The useful-life revision, by contrast, changes NOTHING about last year's already-published depreciation figures — it simply means this year's, and future years', depreciation on that specific machine will be calculated using the shorter 7-year life going forward.
- If a reader doesn't distinguish between these two categories, they might wrongly assume EVERY change to a previously reported number reflects a mistake, undermining confidence in figures that were, in fact, entirely reasonable judgement calls at the time.
- Material prior period error corrections must be specifically disclosed — the nature of the error, the amount of the correction for each prior period presented — precisely so readers can see exactly what changed and why.
What it does to the financial statements
Impact on the P&L
- A change in accounting estimate affects only the current and future periods' P&L — there's no retrospective adjustment to previously reported profit figures, even though the ongoing charge may look meaningfully different from here on.
- A material prior period error requires restating the comparative P&L figures shown alongside the current year's results, so the corrected figures, not the originally incorrect ones, are what readers see.
- A deliberate change in accounting policy, when NOT specifically directed otherwise by a new standard's transition rules, also generally requires retrospective restatement of comparative P&L figures, exactly like an error correction.
- Frequent, unexplained changes in accounting estimates in a direction that flatters reported profit is a pattern some analysts specifically watch for as a potential red flag around the quality of a company's judgement calls.
Impact on the Balance Sheet
- A prior period error correction typically also adjusts the OPENING balance of retained earnings for the earliest period presented, reflecting the cumulative effect of the correction.
- A change in accounting estimate flows through the balance sheet only via its impact on the CURRENT period's figures — there's no adjustment to previously reported balance sheet figures.
- Because prior period error restatements change comparative figures that readers may have already relied upon, they can have real, practical consequences beyond simply 'fixing the books'.
- A pattern of restatements across multiple reporting periods at the same company is generally viewed far more seriously by investors and regulators than a single, well-explained, one-off correction.
Which standard covers this
In India this is governed by Ind AS 8 – Accounting Policies, Changes in Accounting Estimates and Errors, notified under the Companies (Indian Accounting Standards) Rules and applicable to companies that follow Ind AS, setting out the distinct treatment for each of the three categories described in this article.
How it's recognised globally
Globally, the equivalent is IAS 8, and Ind AS 8 mirrors its three-way classification and treatment closely. Under US GAAP, equivalent guidance sits in ASC 250, sharing broadly the same philosophy, though US practice has historically drawn extra public attention to material 'restatements' through specific SEC disclosure requirements (including, for particularly significant errors, a company having to file a formal notification that its previously issued financial statements should no longer be relied upon), giving restatements a somewhat higher public profile in US markets than the broadly comparable Ind AS 8/IAS 8 process typically receives elsewhere.
Real example — Indian listed company
Yes Bank's experience with the Reserve Bank of India's NPA 'divergence' disclosure framework offers a genuinely instructive, real Indian illustration of how a bank's own estimate of loan losses can differ materially from an independent assessor's view, requiring formal disclosure once that gap crosses a regulatory threshold. Under an RBI framework requiring banks to disclose the difference between their own assessment of bad loans and provisioning and the RBI's own supervisory assessment whenever that gap exceeds specified thresholds, Yes Bank disclosed a divergence of roughly ₹4,177 crore in its gross NPA assessment for FY2015-16, and a considerably larger divergence — RBI assessing gross NPAs at roughly ₹8,374 crore against the bank's own reported figure of around ₹2,018 crore for FY2016-17. A further divergence of roughly ₹3,277 crore was disclosed for FY2018-19. While these divergences reflect differing PROVISIONING JUDGEMENTS rather than a straightforward arithmetic error, the scale of the gaps, and the mandatory disclosure they triggered, illustrate vividly why readers of financial statements benefit from understanding exactly how much of a reported number rests on subjective judgement — and why regulators, in banking specifically, have built in an independent check on those judgements.
Where you'll see this
Related concepts
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Segment Reporting
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Events After the Reporting Period (Subsequent Events)
Why something that happens weeks after a company's financial year actually ends can still change the numbers inside financial statements dated for that earlier year-end.