Tax Legal Services · Primary-source case analysis

Thor Power Tool: Financial Accounting Does Not Control Tax Inventory Write-Downs

By Aneeta Mishra and Timothy Chan

Published September 13, 2026

Thor Power Tool Co. v. Commissioner explains the Commissioner’s broad authority to require inventory methods that clearly reflect taxable income even when a company’s books follow generally accepted accounting principles.

The company wrote down excess inventory

Thor reduced the book value of slow-moving spare parts to estimated net realizable value, largely scrap value, while continuing to hold and offer the goods at their original prices. The write-down created a tax loss.

Tax regulations required objective evidence

The inventory regulations generally use cost or lower market and permit submarket valuation in specified circumstances, such as bona fide lower-price offers or defective goods. Thor’s management estimate did not meet those objective conditions.

GAAP and tax accounting serve different purposes

Conservative financial reporting may anticipate losses to protect investors, while tax accounting measures annual taxable income under statutory rules. Conformity with GAAP therefore does not compel acceptance for tax purposes.

The Commissioner’s determination stood

The Court upheld disallowance of the inventory write-down and related additions to a bad-debt reserve. A taxpayer challenging the method must show that the Commissioner’s determination is plainly arbitrary, not merely that another accounting treatment is reasonable.

Key takeaways

• Separate financial-statement policy from tax inventory rules.
• Support below-market valuation with the objective evidence regulations require.
• Document actual offers, defects, or replacement-cost changes.
• Account for the Commissioner’s broad clear-reflection discretion.