IFRS vs US GAAP: The Differences That Actually Matter on a European Audit Engagement

Where the frameworks agree

The two frameworks share more common ground than most practitioners assume. Revenue recognition under IFRS 15 and ASC 606 is largely converged. Both use the five-step model. Business combinations under IFRS 3 and ASC 805 follow the same acquisition method. Fair value measurement under IFRS 13 and ASC 820 uses the same three-level hierarchy. Earnings per share under IAS 33 and ASC 260 produce the same numbers in most scenarios.

The Deloitte 2025 edition of their IFRS vs US GAAP comparison notes that differences between the two frameworks tend to arise from the level of specific guidance provided rather than from fundamentally different principles. IFRS is more principles-based. US GAAP provides more rules and industry-specific guidance. For converged standards, the accounting outcome is usually the same. The differences that actually affect your file sit in the areas where convergence either failed or was never attempted.

Inventory: the LIFO problem

IAS 2.25 permits FIFO and weighted-average cost. It does not permit LIFO (last-in, first-out). US GAAP (ASC 330) permits all of these, including LIFO. Many US companies use LIFO because it reduces taxable income in periods of rising prices (the IRS requires LIFO conformity: if you use it for tax, you must use it for financial reporting).

When converting a US subsidiary that uses LIFO, the adjustment is straightforward in concept but can be material. The subsidiary will disclose a “LIFO reserve” in its notes (ASC 330 requires it). The LIFO reserve represents the difference between LIFO inventory and what it would have been under FIFO. To convert, you add the LIFO reserve back to inventory on the balance sheet and adjust cost of sales in the income statement by the change in the LIFO reserve during the period. The tax effect runs through deferred tax.

On a typical mid-market manufacturing subsidiary, the LIFO reserve can run from 5% to 25% of total inventory value. If inventory is material to the group, this is not a rounding difference. Document it as a conversion entry, verify the LIFO reserve disclosure in the US GAAP financial statements, and recalculate the income statement effect.

Impairment reversal: the one-way street under US GAAP

IAS 36.114 requires reversal of an impairment loss on assets other than goodwill when the conditions that caused the impairment no longer exist. US GAAP (ASC 360-10-35) prohibits reversal of impairment losses on long-lived assets. Once written down, the asset stays at its reduced carrying amount. Both frameworks prohibit reversal of goodwill impairment.

This difference matters when a US subsidiary impaired an asset in a prior year and conditions have since improved. Under US GAAP, the carrying amount stays at the impaired value. Under IFRS, you must assess whether the reversal criteria in IAS 36.110 are met and, if so, reverse up to the carrying amount that would have existed (net of depreciation) had the impairment never been recognised. The reversal goes through profit or loss.

For the auditor, this creates an adjustment that has no US GAAP counterpart. You cannot rely on the US subsidiary’s impairment testing alone. You need to separately assess whether IAS 36 reversal indicators exist for any previously impaired asset and calculate the reversal amount if they do.

Development costs: capitalise or expense?

IAS 38.57 requires capitalisation of development costs when six criteria are met: technical feasibility, intention to complete, ability to use or sell, probable future economic benefits, availability of resources, and ability to measure expenditure reliably. If all six are met, capitalisation is mandatory, not optional. US GAAP (ASC 730) generally requires all research and development costs to be expensed as incurred, with narrow exceptions for software development costs under ASC 985-20 (external-use software) and ASC 350-40 (internal-use software).

In practice, this difference produces permanently different balance sheets. A technology subsidiary reporting under US GAAP will show zero capitalised development on its balance sheet. The same subsidiary under IFRS might capitalise a significant portion of its later-stage development spending. When converting, you need to:

1. Identify which development expenditures meet the IAS 38.57 criteria
2. Determine the point at which the criteria were first met (the “trigger date”)
3. Capitalise all qualifying costs from that date forward
4. Apply amortisation from the date the asset was available for use
5. Test for impairment under IAS 36

This is not a simple journal entry. It requires access to the subsidiary’s project-level cost records and a judgment call on when the six criteria were satisfied. On a first-year conversion, expect this to be one of the most time-intensive adjustments.

Leases: one model vs two

IFRS 16 applies a single lessee accounting model. Every lease (with exceptions for short-term and low-value leases) goes on the balance sheet as a right-of-use asset and lease liability. The income statement shows depreciation on the asset and interest on the liability. US GAAP (ASC 842) maintains a dual model. Finance leases receive balance sheet treatment similar to IFRS 16. Operating leases also go on the balance sheet (a change from ASC 840), but the income statement treatment differs: operating leases produce a single straight-line lease expense rather than the front-loaded depreciation-plus-interest pattern.

The balance sheet numbers are similar under both frameworks. The income statement difference is where the conversion adjustment sits. A US subsidiary with large operating leases will report a flat lease expense each period. Under IFRS, the same leases produce higher total expense in earlier years (because interest on the declining liability is higher at the start) and lower total expense in later years. Over the full lease term, total expense is the same. In any given period, it differs.

For the auditor, the conversion requires recalculating the income statement pattern for every material operating lease. If the subsidiary has recently entered into large leases, the difference can be significant in the current period.

Income statement presentation: IFRS 18 vs US GAAP

This is where the gap is widening. IFRS 18 (effective 1 January 2027) introduces five mandatory categories for income and expenses (operating, investing, financing, income taxes, discontinued operations) with required subtotals for operating profit and profit before financing and income taxes. “Operating profit” becomes a defined, comparable term across all IFRS reporters.

US GAAP has no equivalent reform. The FASB issued ASU 2024-03 (effective for fiscal years beginning after 15 December 2026), which requires public business entities to disaggregate certain income statement expense line items in the notes. But it does not prescribe categories in the income statement itself. US GAAP still does not define “operating income” at the standard level, although SEC Regulation S-X requires certain line items for registrants.

For European auditors, the practical consequence is that comparing an IFRS group’s income statement to a US GAAP peer will become harder after 2027, not easier. The IFRS income statement will have a prescribed structure. The US GAAP income statement will not. If your client benchmarks against US peers or if investors compare across frameworks, document the structural difference in your analytical review working papers. Ratios calculated from “operating profit” will not be comparable across frameworks.

Financial instruments: business model vs intent

IFRS 9 classifies financial assets based on the entity’s business model for managing the assets and the contractual cash flow characteristics of the asset. The business model test is entity-wide: is the objective to hold to collect, to hold to collect and sell, or other? US GAAP (ASC 320 and ASC 321) classifies debt securities based on management’s intent and ability (held-to-maturity, available-for-sale, trading). Equity securities without readily determinable fair values get a practical expedient under ASC 321.

The measurement outcomes are often similar. Both frameworks measure trading instruments at fair value through profit or loss. Both allow amortised cost for instruments held to collect (US GAAP: held-to-maturity). The differences sit at the boundary: IFRS 9’s “fair value through other comprehensive income” (FVOCI) election for equity instruments is irrevocable and has no US GAAP parallel. IFRS 9’s expected credit loss model uses a lifetime ECL trigger based on significant increase in credit risk. US GAAP’s current expected credit loss model (ASC 326, “CECL”) requires lifetime expected losses from day one.

On the IFRS 9 ECL calculator, you can model the difference between incurred loss, IFRS 9 staging, and day-one lifetime loss approaches. For conversion engagements, the ECL model is typically the largest financial instruments adjustment.

Worked example: converting a US subsidiary for IFRS consolidation

Client: De Graaf Precision B.V., a Dutch engineering group with €94M consolidated revenue. De Graaf acquired ProTech Inc., a US-based manufacturer reporting under US GAAP, in 2024 for €18M. ProTech has €6.2M in inventory (LIFO), €1.1M in previously impaired equipment (written down from €1.8M in 2023, conditions have since recovered), €0.4M in R&D expense (of which €0.15M relates to development activity meeting IAS 38.57 criteria since Q2 2025), and four operating leases totalling €2.8M in right-of-use assets.

Adjustment 1: Inventory (LIFO to FIFO)

ProTech’s LIFO reserve is €0.74M per its US GAAP notes. Add €0.74M to inventory on the balance sheet. The change in the LIFO reserve during 2025 was €0.09M (increase), so reduce cost of sales by €0.09M. Recognise deferred tax liability on the adjustment at the US federal rate of 21%: €0.74M x 21% = €0.155M.

Adjustment 2: Impairment reversal

The equipment was impaired by €0.7M in 2023 under ASC 360. Conditions have recovered. Under IAS 36.114, the reversal is permitted. The carrying amount had the impairment never occurred would be €1.5M (original €1.8M less two years of depreciation at €0.15M/year). Current carrying amount is €0.8M (impaired value of €1.1M less one year depreciation of €0.3M). Reversal amount: €0.7M, capped at €1.5M minus €0.8M = €0.7M. Recognise in profit or loss.

Adjustment 3: Development cost capitalisation

Of ProTech’s €0.4M R&D expense, €0.15M relates to development activity that met the IAS 38.57 criteria from Q2 2025. Capitalise €0.15M as an intangible asset. The asset is not yet available for use, so no amortisation in the current period. Test for impairment indicators under IAS 36.

Adjustment 4: Lease income statement reclassification

ProTech’s four operating leases produce a straight-line expense of €0.62M under ASC 842. Under IFRS 16, the same leases produce depreciation of €0.56M plus interest of €0.11M = €0.67M. The current-year conversion adjustment increases total expense by €0.05M, with a corresponding change in the right-of-use asset and lease liability carrying amounts.

Total impact on group profit before tax: +€0.09M (inventory) +€0.7M (impairment reversal) +€0.15M (development capitalisation) −€0.05M (lease timing) = +€0.89M. This is material relative to De Graaf’s group PBT of €7.1M (12.5% impact).

Practical checklist for your file

1. On any engagement where the group consolidates a US GAAP subsidiary, prepare a conversion memo listing every identified IFRS vs US GAAP difference. Classify each as material or immaterial to the group.
2. Check for LIFO inventory. If present, obtain the LIFO reserve from the US GAAP notes, adjust inventory and cost of sales, and compute the deferred tax effect.
3. Review any prior-year impairments on the US subsidiary’s long-lived assets. Assess whether IAS 36.110 reversal indicators exist. If they do, calculate the reversal amount.
4. Obtain project-level R&D cost records for any material development activity. Assess the IAS 38.57 trigger date and capitalise qualifying costs from that point forward.
5. Recalculate the income statement pattern for material operating leases under IFRS 16. The balance sheet treatment is similar; the income statement timing differs.
6. Document whether IFRS 18 income statement categories (effective 2027) will create additional presentation differences beyond the measurement adjustments.

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Frequently asked questions

Further reading and source references

• Deloitte: IFRS and US GAAP: A Pocket Comparison (2025 edition) – comprehensive side-by-side analysis of differences across all major standard areas.
• IAS 36, Impairment of Assets – reversal requirements at paragraphs 110–119.
• IAS 38, Intangible Assets – development cost capitalisation criteria at paragraph 57.
• IFRS 18, Presentation and Disclosure in Financial Statements (issued April 2024, effective 1 January 2027) – the five income statement categories and mandatory subtotals.
• FASB ASU 2024-03, Disaggregation of Income Statement Expenses (effective for fiscal years beginning after 15 December 2026) – expense line-item disaggregation in notes.