A recent Norwegian Supreme Court case cuts to the heart of a question that does not come up often enough in transfer pricing practice: how do thin capitalisation rules interact with the arm’s length principle when pricing intercompany debt?
At first glance, thin cap may feel like a separate discipline. But where it operates through the arm’s length principle, it becomes inseparable from transfer pricing, and this case shows exactly why.
The Case at a Glance
A Norwegian entity borrowed from a related party at a rate, and in an amount, the Norwegian Tax Administration (NTA) considered non-arm’s length. The NTA identified excess debt under thin cap principles but then applied the actual above-market interest rate to that excess debt when calculating the disallowed deduction. The case made its way to Norway’s Supreme Court, which ruled in March 2026.
How the Adjustment Was Built
The Tax Authority’s Approach
The NTA split the analysis in two. It reduced the level of debt to what it considered arm’s length, but retained the original, higher interest rate when calculating the adjustment. This resulted in a larger transfer pricing adjustment and increased income tax exposure.
Why That Approach Fails
At first glance, the logic might seem acceptable: adjust the debt, keep the rate. But this ignores a fundamental point. Debt level and interest rate are not independent variables. They are economically linked, and treating them separately produces a distorted result.
What the Court Decided
The Supreme Court rejected the NTA’s approach entirely.
The Arm’s Length Reconstruction Principle
The Court emphasised that applying the arm’s length principle requires reconstructing the transaction in its entirety. That means determining not only how much debt an independent lender would provide, but also at what rate that debt would be priced. Both elements must be determined simultaneously, not in isolation.
The Correct Method
Step 1: Determine arm’s length debt
Apply thin cap analysis to establish the debt level an independent lender would have provided.
Step 2: Recalculate the borrower’s credit profile
With a lower debt level, the borrower’s leverage changes, and so does its credit risk.
Step 3: Determine the arm’s length interest rate
Price the debt based on the revised credit profile, not the original over-leveraged position.
Step 4: Compute the disallowed deduction
The adjustment is: Actual Interest minus (Arm’s Length Debt multiplied by Arm’s Length Rate).
Using this method, the taxpayer’s adjustment was significantly lower. The taxpayer won.
Why This Thin Cap Ruling Matters
Thin Cap Adjustments Must Reflect Arm’s Length Pricing
The most important takeaway is understanding why debt level affects the interest rate. Interest rates are derived from credit analysis, and credit analysis depends heavily on leverage. A more leveraged borrower presents higher risk and attracts a higher rate. A less leveraged borrower presents lower risk and attracts a lower one. Once thin cap reduces the level of debt, the borrower’s credit profile must change accordingly.
The Double Distortion Problem
The NTA’s approach applied a lower debt level but retained a higher, over-leveraged interest rate. This stacked two distortions against the taxpayer simultaneously, and the Court correctly rejected it. Each distortion on its own might have been defensible. Together, they produced an outcome that did not reflect what independent parties would have agreed.
What This Means for Transfer Pricing Practice
Thin Cap and Arm’s Length Cannot Be Separated
Where thin capitalisation operates through the arm’s length principle, it is inherently a transfer pricing issue. Debt quantum and debt pricing are a package and cannot be analysed in isolation. A transfer pricing team that treats them separately is working with an incomplete framework.
Credit Analysis Must Reflect Arm’s Length Leverage
Benchmarking an interest rate against an over-leveraged borrower leads to flawed comparability analysis. The hypothetical borrower used in the analysis must reflect an arm’s length capital structure, consistent with what unrelated parties would actually agree to.
Your Analyses Must Talk to Each Other
A key risk highlighted by this case is inconsistency between workstreams. If the debt capacity study and the interest rate benchmarking are performed independently without alignment, the resulting documentation contains vulnerabilities that tax authorities can exploit. The Norwegian case is a clear example of what happens when those two analyses are not connected.
Managing Intercompany Financing in Practice
Ensuring consistency across intercompany financing arrangements requires more than running two separate analyses. The assumptions underlying debt capacity and interest rate benchmarking need to be aligned, the credit modelling needs to reflect the correct leverage position, and the documentation needs to show clearly how debt level and pricing interact.
When those elements are not connected, what appears to be a technical mismatch can quickly become a material transfer pricing risk during an audit.
Reptune helps multinational tax teams centralise financial data, align debt capacity and pricing analyses, and maintain consistency across jurisdictions. When a tax authority challenges the structure, the analysis is already integrated and the documentation reflects a coherent, defensible position.
Final Takeaway
The Norwegian Supreme Court’s ruling is a reminder that transfer pricing adjustments must reflect economic reality in full, not selectively. Reconstructing a transaction under the arm’s length principle means reconstructing all of it. Adjusting one variable while leaving another unchanged does not produce an arm’s length outcome. It produces a distortion, and as this case shows, courts will see through it.
