Change in Accounting Principle vs Estimate vs Error: Retrospective or Prospective?

A company that switches from straight-line to double-declining depreciation has changed its accounting principle, and every candidate's instinct is to restate the prior years. ASC 250 says the opposite: a change in depreciation method is accounted for as a change in estimate, prospectively, with nothing restated. It is the one exception in the topic that reverses the answer, and it is examined more often than any rule in it.

The topic is small and entirely decidable. There are three kinds of change, two directions in time, one exception, one escape clause and one entry. What makes it worth marks is that each kind looks like the others in a fact pattern, and the question is almost always "which is it?" before it is "what is the number?"

The three kinds

Kind	What it is	Direction	Examples
Change in accounting principle	A switch from one acceptable method to another acceptable method	Retrospective	LIFO to FIFO; completed-contract to percentage-of-completion; a new standard's transition
Change in accounting estimate	A revision of a judgement about the future as new information arrives	Prospective	Useful life, salvage value, bad-debt percentage, warranty rate, and any change in depreciation method
Correction of an error	A mistake in a prior period: arithmetic, misapplied GAAP, a fact overlooked, an unacceptable method	Restatement	Expensing a capital asset; missing an accrual; cash-basis to accrual

A fourth category, a change in the reporting entity, is retrospective like a change in principle and appears rarely; it covers presenting consolidated statements in place of individual ones and changing the set of subsidiaries consolidated.

The first decision in any question is the distinction between the first row and the third. A switch from a method that was never acceptable, cash basis for a company that should have accrued, is not a change in principle: it is an error. A switch between two acceptable methods is a change in principle, and ASC 250 requires that the new method be preferable, with the justification disclosed.

Change in principle: retrospective

Retrospective application means the financial statements are presented as though the new principle had always been used. Three things happen.

1. Every prior period presented is recast under the new principle.
2. The cumulative effect on periods before the earliest one presented is booked as an adjustment to the opening balance of retained earnings of that earliest period, net of tax.
3. The change, its reason, the method of applying it, and its effect on each line item and on EPS are disclosed for every period presented.

The entry. A company changes from LIFO to FIFO at the start of 20X3 and presents 20X2 and 20X3. FIFO inventory at the end of 20X1 would have been 300,000 higher than LIFO. The tax rate is 25%. The opening retained earnings of 20X2, the earliest period presented, are adjusted by 300,000 less 75,000 of deferred tax: debit inventory 300,000, credit deferred tax liability 75,000, credit retained earnings 225,000. The 20X2 statements are then recast under FIFO in full.

Direct and indirect effects. Only the direct effects, the inventory and its tax, go into the retrospective adjustment. Indirect effects, such as a profit-sharing payment that would have been different under FIFO, are recognised in the period the change is made, not pushed back.

The impracticability clause. If the cumulative effect cannot be determined, ASC 250 allows the new principle to be applied from the earliest date practicable, and if even the period-specific effects cannot be determined, prospectively. The classic case is the reverse of the entry above: a change to LIFO. Rebuilding LIFO layers for prior years is usually impracticable, so the opening inventory of the year of change becomes the first LIFO layer and nothing is restated. A question that describes a change to LIFO and offers a retained earnings adjustment as an answer is offering a distractor.

Change in estimate: prospective

A change in estimate is accounted for in the period of change and, where it affects them, future periods. No prior period is touched, no retained earnings entry is made, and the disclosure is the effect on the current period's income and EPS if material (routine estimate changes, such as an annual revision of bad debts, need no disclosure at all).

The computation. An asset cost 1,200,000 with a ten-year life, no salvage, straight-line. After three years, book value is 840,000. Management now estimates four years remaining and a salvage value of 100,000. Depreciation from year four is 840,000 less 100,000, divided by four: 185,000 per year. The first three years' charge of 120,000 stays exactly where it was.

The rule generalises: take the current book value, apply the new estimate, and go forward. Every estimate question in FAR is that sentence with different numbers.

The depreciation method exception

A change in depreciation, amortisation or depletion method is a change in principle by nature, but ASC 250 treats it as "a change in accounting estimate effected by a change in accounting principle," and the accounting is that of an estimate: prospective. The reasoning is that the choice of method reflects an estimate of the pattern in which the asset's benefits are consumed, and revising it is revising that estimate. The company still has to justify the new method as preferable, so the disclosure resembles a change in principle, but the numbers do not. Straight-line to double-declining: book value forward, new method, no restatement.

The inseparable rule

When a change in principle cannot be separated from a change in estimate, the whole change is treated as a change in estimate. The standard example is a change from deferring and amortising a cost to expensing it as incurred, made because the future benefits have become doubtful. The new principle (expense) and the new estimate (no future benefit) are one decision, and the accounting is prospective.

Error correction: restatement

An error discovered after the statements were issued is corrected by restating the prior-period statements. The mechanics mirror a change in principle: prior periods presented are corrected, the cumulative effect on earlier periods goes to opening retained earnings of the earliest period presented as a prior-period adjustment, net of tax, and the nature of the error and its effect on each line item and EPS are disclosed. The word "restatement" is reserved for errors; a change in principle is "retrospective application." Using the wrong word in a simulation response is a way to lose a mark that is otherwise free.

The entry. Equipment costing 200,000 with a five-year life and no salvage was expensed on purchase on 1 January 20X2. The error is found in 20X3. The 20X2 income was understated by 200,000 less one year's depreciation of 40,000. If 20X2 is presented, it is restated; if it is not, the opening retained earnings of 20X3 are increased by 160,000 pre-tax: debit equipment 200,000, credit accumulated depreciation 40,000, credit retained earnings 160,000, with the tax effect against the deferred tax account.

Counterbalancing errors. Some errors reverse themselves in two years. An overstatement of ending inventory in 20X2 overstates 20X2 income and understates 20X3 income by the same amount; by the end of 20X3, retained earnings are correct. The exam's question is whether an entry is needed, and the answer depends on when the error is found. Found during 20X3 before the books close, retained earnings and inventory (or cost of sales) are corrected. Found after 20X3 closes, no entry is needed for the balance sheet, though the prior-year statements are still restated if presented.

The decision table

Fact pattern	Category	Treatment
FIFO to weighted average	Principle	Retrospective; opening retained earnings of earliest period
FIFO to LIFO	Principle, impracticable	Prospective from the opening inventory of the year of change
Straight-line to sum-of-years'-digits	Estimate effected by principle	Prospective from current book value
Useful life 10 years to 7	Estimate	Prospective
Warranty accrual 2% to 3% of sales	Estimate	Prospective
Percentage-of-completion adopted for existing contracts	Principle	Retrospective
Accrued salaries omitted last year	Error	Restatement; prior-period adjustment
Cash basis to accrual basis	Error	Restatement
Consolidating a subsidiary previously excluded	Reporting entity	Retrospective
New FASB standard with prescribed transition	Principle	As the standard's transition provisions require

IAS 8, for the IFRS reader

An IFRS-trained candidate will find the structure identical, because IAS 8 was the model. The same three categories, retrospective for policies, prospective for estimates, restatement for prior-period errors, the same impracticability exception, and the same landing place in opening equity of the earliest period presented. Three differences are worth noting.

IAS 8 requires a voluntary change in policy to result in information that is "reliable and more relevant," where ASC 250 asks for "preferable"; the exam uses the US word. IAS 8 restates only material prior-period errors, and its 2021 amendment, effective from 2023, defines accounting estimates as "monetary amounts in financial statements that are subject to measurement uncertainty," so that a change in a valuation technique or an input is a change in estimate; ASC 250 reaches the same answer through the depreciation exception and the inseparable rule. And IAS 8 does not have a separate "change in reporting entity" category. None of the three changes the numbers in a FAR question.

Where to practise this

The topic is a classification skill followed by one computation, and it is learned by classifying fifty fact patterns quickly. Prepito's FAR course covers ASC 250 with practice questions and simulations that ask for the category, the entry and the disclosure, with a full explanation of why each distractor is wrong. The SOCPA Financial Accounting course covers the same ground under IAS 8. The FAR study guide shows where the topic sits in the blueprint.

---

Sources: FASB Accounting Standards Codification, Topic 250, Accounting Changes and Error Corrections, IFRS Foundation, IAS 8 Accounting Policies, Changes in Accounting Estimates and Errors, AICPA CPA Exam Blueprints. Worked entries are illustrative; confirm the current text of ASC 250 and any standard's own transition provisions for a specific case.