Introduction: Corporate Interest Restriction and Your UK Company
The corporate interest restriction denies UK companies relief for interest they have genuinely paid, and American owners meet it later than anyone else. Furthermore, they usually meet it twice. Britain applies its corporate interest restriction, and the United States restricts the very same borrowing under section 163(j).
Most guidance treats these as separate worlds. However, the two regimes now interact badly, and a change effective in 2026 makes the overlap materially worse for anyone holding a UK company. At TaxYork, we model both together, because clients who model only one consistently underestimate the cost.
Why the Corporate Interest Restriction Reaches American Owners
Leverage is the common factor. Specifically, Americans who build UK property groups, acquire trading companies or fund expansion through debt all accumulate interest expense. Consequently, the corporate interest restriction becomes relevant far sooner than they expect.
The rules are not confined to multinationals. Additionally, a single American individual can constitute a worldwide group for these purposes. Therefore, a structure that feels modest by global standards still falls squarely inside the corporate interest restriction.
What Changed for 2026
Two developments matter this year. Firstly, the administrative deadline for appointing a reporting company altered for periods ending on or after 31 March 2026. Secondly, and far more expensively, the American calculation changed on 1 January 2026.
That second change removes controlled foreign corporation income from the US limitation base. Consequently, owners of UK companies lost capacity precisely because they own UK companies. We explain the mechanics below, with worked figures throughout.
How the Corporate Interest Restriction Actually Works
The regime sits in Part 10 of TIOPA 2010, introduced by Finance (No. 2) Act 2017. It applies to periods of account beginning on or after 1 April 2017.
The £2 Million De Minimis Everyone Relies On
A single threshold protects most smaller groups. Specifically, the corporate interest restriction bites only where a worldwide group has aggregate net tax-interest expense above £2 million in a twelve-month period. Below that figure, no disallowance arises.
The allowance belongs to the group rather than the company. Furthermore, it is pro-rated for periods shorter than twelve months. Consequently, a group with four leveraged subsidiaries shares one £2 million threshold between them, not four.
Rising rates changed who qualifies. Notably, groups that sat comfortably below the threshold at historic Bank of England rates now exceed it on identical borrowing. Therefore, the de minimis protects far fewer American-owned structures than it did five years ago.
The Fixed Ratio and Tax-EBITDA
Groups above the threshold apply the fixed ratio rule. Specifically, deductible interest is capped at 30% of UK tax-EBITDA, which is taxable earnings before interest, tax, depreciation and amortisation as computed for tax purposes.
Tax-EBITDA is not accounting EBITDA. Moreover, it excludes items that never enter the UK tax computation at all. Consequently, a property group with large non-taxable revaluation movements often finds its tax-EBITDA far smaller than its accounts suggest.
A second ceiling also applies. Additionally, relief cannot exceed the group's adjusted net worldwide interest expense to third parties. Therefore, the corporate interest restriction limits you to the lower of the two measures.
The Group Ratio Alternative
Highly geared groups may elect out of the fixed ratio. Specifically, HMRC guidance permits a group ratio election, which substitutes the group's own external gearing for the flat 30%.
The election frequently rescues property structures. For example, a group whose worldwide external interest represents 45% of its group EBITDA may deduct at that higher percentage. Nevertheless, the election is annual and irrevocable for the period, so modelling matters before you file.
What Counts as Tax-Interest
Definitions are wider than clients assume. Notably, tax-interest captures amounts economically equivalent to interest, including the finance element of leases, guarantee fees and certain derivative flows. The HMRC glossary sets out the terminology.
Shareholder debt counts too. Furthermore, interest on loans from the American owner personally falls within the corporate interest restriction exactly as bank debt does. Consequently, funding a UK company through director loans provides no escape from the corporate interest restriction.
Which Structures Actually Trigger the Corporate Interest Restriction
Exposure varies enormously by sector, and the pattern surprises most owners.
Why Property Groups Suffer Most
Property investment is the classic casualty. Specifically, rental businesses combine heavy leverage with modest taxable earnings, which is precisely the combination the fixed ratio punishes. Consequently, the corporate interest restriction bites hardest where borrowing is most commercially normal.
Depreciation offers no rescue either. Furthermore, UK investment property attracts no capital allowances on the structure itself, so tax-EBITDA stays close to net rental profit. Therefore, a group paying £4 million of interest on £8 million of rents faces disallowance almost automatically.
Trading Companies and Holding Companies
Trading groups fare better. Notably, a profitable trading business generates substantial tax-EBITDA relative to its debt, so the 30% ceiling rarely binds. Additionally, capital allowances add back into the measure, lifting capacity further.
Pure holding companies sit at the opposite extreme. Meanwhile, a holdco with dividend income and acquisition debt has almost no tax-EBITDA at all, because UK dividends are largely exempt. Consequently, acquisition debt pushed into a holding company is frequently disallowed in full.
Why One American Can Be a Worldwide Group
The group definition catches individuals. Specifically, HMRC guidance on group membership looks to consolidation under accounting standards, and a single ultimate parent brings its subsidiaries together. An American who owns several UK companies through one vehicle therefore holds a worldwide group.
The consequence is a shared threshold. Furthermore, the £2 million allowance covers every company beneath that parent. Therefore, splitting a portfolio across multiple companies achieves nothing against the corporate interest restriction, though it remains useful for other reasons.
Carry-Forwards, Reactivation and the Five-Year Cliff
Disallowance is rarely permanent, provided you preserve the position properly.
Disallowed Interest Carries Forward Without Limit
A disallowance does not destroy the deduction. Instead, the disallowed amount becomes an attribute of the company that suffered it, and it carries forward indefinitely. No time limit applies at all.
The attribute stays with that company. Therefore, group reorganisations can strand relief in an entity that no longer generates capacity. Additionally, the amount only returns to use through reactivation, which we explain below.
Unused Allowance Expires After Five Years
The opposite attribute behaves differently. Specifically, where the group's interest allowance exceeds its interest expense, the surplus carries forward for five years only. Brought forward allowance then time-expires.
This asymmetry punishes inattention. Moreover, a group that swings between surplus and deficit years can watch allowance expire while disallowance sits unused elsewhere. Consequently, sequencing acquisitions and refinancings around the five-year window produces real savings.
Why Reactivation Rewards Good Records
Reactivation happens at company level. Specifically, interest reactivation capacity arises when the group's interest allowance exceeds its aggregate net tax-interest expense. The reporting company then allocates that capacity.
Nothing happens automatically. Furthermore, reactivation requires a return that claims it. Therefore, groups that stopped filing after a quiet year frequently forfeit relief they had already earned under the corporate interest restriction.
Compliance: Reporting Companies and Returns
The administrative rules trap more American owners than the arithmetic does.
Appointing a Reporting Company After March 2026
Every group above the threshold needs a reporting company. Historically, groups had twelve months from the end of the first period of account to appoint one. However, for periods ending on or after 31 March 2026, that time limit no longer applies.
The relaxation helps late arrivals considerably. Nevertheless, HMRC retains power to appoint a reporting company itself. Consequently, waiting is still a poor strategy, because a revenue appointment removes your control over elections.
Full Returns and Abbreviated Returns
Two return types exist. Specifically, a full interest restriction return is required where a disallowance arises, while an abbreviated return suffices where the group merely wishes to preserve allowance. Both fall due twelve months after the period end.
Choosing wrongly costs money. Additionally, an abbreviated return cannot claim reactivation. Therefore, groups expecting to recover disallowed amounts must file in full, even where the current year shows no restriction.
What Happens If You File Nothing
Silence has consequences. Firstly, the group loses the ability to make elections, including the group ratio election that often halves the charge. Secondly, HMRC may apply the default position, which assumes no elections at all.
Penalties then follow the corporation tax regime. Meanwhile, the underlying corporate interest restriction disallowance still stands, so the tax is due regardless. Consequently, the cheapest compliance failure we see still costs six figures.
The American Half: Section 163(j)
Britain is only half the problem, and the American half is currently deteriorating.
Thirty Per Cent of Adjusted Taxable Income
Section 163(j) limits deductible business interest to the sum of business interest income, 30% of adjusted taxable income and floor plan financing interest. The structure deliberately mirrors the UK fixed ratio.
A small business exemption exists. Specifically, taxpayers meeting the section 448(c) gross receipts test escape entirely, and that threshold is $32 million for 2026. However, aggregation rules combine related entities, so multiple companies rarely help.
The EBITDA Add-Back Restored From 2025
The base became more generous recently. Specifically, for tax years beginning after 31 December 2024, taxpayers add back depreciation, amortisation and depletion when computing adjusted taxable income. The IRS guidance on the change confirms the position.
That restoration is permanent. Furthermore, it brings the American measure closer to the UK tax-EBITDA concept. Consequently, capital-intensive businesses regained substantial capacity, which is genuinely welcome news.
The 2026 Change That Punishes CFC Owners
The good news came with a sting attached, and it lands this year. For tax years beginning after 31 December 2025, adjusted taxable income excludes amounts under sections 951(a) and 951A(a), together with section 78 gross-ups and associated deductions.
Read that carefully. Specifically, Subpart F income and net CFC tested income no longer swell your American limitation base. Therefore, an American whose UK subsidiary generates large inclusions has just lost the capacity those inclusions used to create, while the underlying debt remains unchanged.
The irony is complete. Moreover, the very ownership that triggers Form 5471 reporting now shrinks your interest deduction. Consequently, 2026 is the first year in which owning a UK company actively worsens your section 163(j) position.
Carryforwards Without Expiry
American disallowance behaves like the British version. Specifically, disallowed business interest carries forward indefinitely and is reported on Form 8990. No five-year cliff applies.
The comfort is limited in practice. Additionally, a structure that is permanently over-leveraged never generates the capacity to release the carryforward. Therefore, indefinite carryforward often means indefinite deferral rather than eventual relief.
Where the Two Restrictions Collide
The interaction is where American owners lose money that neither system intended to take.
Double Disallowance on the Same Interest
Consider the mechanics honestly. Firstly, the UK group suffers a corporate interest restriction disallowance on its own borrowing. Secondly, the American holding company suffers a section 163(j) disallowance on its separate borrowing.
Neither restriction relieves the other. Furthermore, no treaty article addresses interest limitation rules at all. Consequently, the same commercial leverage strategy is penalised twice, in two currencies, under two sets of carry-forward rules.
The Foreign Tax Credit Consequence
The credit cannot bridge the gap. Specifically, a UK disallowance increases UK corporation tax at the 25% main rate, which does generate creditable foreign tax on Form 1118. So far, so reasonable.
The difficulty is the limitation. However, the foreign tax credit is capped by US tax on foreign-source income in the relevant basket. Consequently, extra UK tax arising from a corporate interest restriction disallowance frequently exceeds the available limitation and strands as excess credit.
Timing Mismatches Between the Regimes
Periods rarely align. Notably, the UK operates on periods of account while the American rules follow the taxpayer's tax year. Additionally, group boundaries differ, because the UK worldwide group and the US consolidated group are defined separately.
Those differences compound. Therefore, interest disallowed in Britain in one year may correspond to American relief in a different year entirely. Meanwhile, the foreign tax credit demands matching that the two regimes actively prevent.
Individual Landlords: The Other Restriction
Many American clients hold UK property personally rather than corporately, and a different rule applies to them.
Section 272A and the Basic Rate Reducer
Individuals cannot deduct residential finance costs at all. Specifically, section 272A of ITTOIA 2005 removes them from the profit computation, and relief arrives instead as a basic rate tax reducer under section 274A.
The effect inflates taxable profit. Furthermore, HMRC's calculation guidance shows how the reducer applies after the tax computation. Consequently, a higher rate landlord suffers tax on income that never reached their bank account.
The Rise to 22% in April 2027
The reducer is currently 20%. However, it rises to 22% from 6 April 2027, tracking the new property basic rate. Therefore, the restriction softens modestly, though it remains far from full relief for additional rate taxpayers.
Planning horizons should reflect this. Additionally, the change affects the arithmetic of incorporating a portfolio. Consequently, clients weighing a transfer into a company should model both the reducer and the corporate interest restriction that would then apply.
Why This Wrecks the Foreign Tax Credit
Here lies the trap that catches Americans specifically. The United States allows a full deduction for the mortgage interest on a rental property. Meanwhile, Britain denies it and grants a partial credit instead.
The bases therefore diverge sharply. Consequently, UK taxable rental profit is far higher than the American figure, so UK tax often exceeds the US tax on the same property. That excess strands in the passive basket, exactly as a corporate interest restriction disallowance does at company level.
The Rules That Apply Before the Corporate Interest Restriction
Ordering matters enormously, because three other regimes reduce your interest first.
Transfer Pricing Comes First
Related-party debt faces an earlier test. Specifically, UK transfer pricing asks what an independent lender would have advanced on arm's length terms. Anything above that figure is disallowed before the corporate interest restriction is even computed.
Americans funding UK companies routinely trip this. Moreover, a shareholder loan at a generous rate, or on terms no bank would offer, is adjusted downward first. Consequently, clients sometimes discover that two separate rules have each removed a slice of the same interest.
The Unallowable Purpose Rule
A second gatekeeper applies to purpose. Specifically, section 441 of CTA 2009 denies debits on a loan relationship with an unallowable purpose, meaning a main purpose of securing a tax advantage. Recent tribunal decisions have applied it far more aggressively than practitioners once expected.
Commercial documentation is the defence. Additionally, contemporaneous board minutes recording genuine commercial rationale carry real weight. Therefore, the paperwork supporting an intra-group loan deserves the same care as the paperwork supporting the rate.
Hybrid Mismatches and US Structures
The third regime targets American structures specifically. Notably, Part 6A of TIOPA 2010 counteracts hybrid mismatches, and check-the-box elections create exactly the entity classification differences it addresses. A US LLC treated as transparent in America and opaque in Britain is a standard trigger.
The counteraction can be severe. Furthermore, it may deny the UK deduction entirely, regardless of any remaining capacity under the corporate interest restriction. Consequently, any American-owned structure using disregarded entities should be reviewed against Part 6A before leverage is added, and the US Treasury policy materials provide useful background on the wider international framework.
Case Study: An American-Owned London Property Group
Consider an illustrative scenario drawn from work we see regularly.
The Facts
An American investor holds four UK property companies beneath a Delaware holding company. The UK group carries £62 million of external debt at a blended 6.4%, producing net tax-interest expense of £3.97 million. Its UK tax-EBITDA for the period is £8.2 million.
The Delaware company borrowed separately. Specifically, it holds $18 million of acquisition debt at 7%, giving $1.26 million of American interest expense. Group gross receipts comfortably exceed the $32 million small business threshold.
The Corporate Interest Restriction Calculation
The de minimis offers nothing here. Firstly, net tax-interest of £3.97 million far exceeds £2 million. Secondly, the fixed ratio permits only 30% of £8.2 million, which is £2.46 million.
The disallowance therefore reaches £1.51 million. Consequently, additional UK corporation tax at 25% comes to £377,500. However, a group ratio election reflecting worldwide external gearing of 38% lifted the allowance to £3.12 million.
That election reduced the disallowance to £850,000. Accordingly, the corporate interest restriction cost fell to £212,500, saving £165,000 for the price of a timely return.
The US Position and the Combined Cost
The American side deteriorated simultaneously. Previously, the Delaware company's adjusted taxable income included $4.1 million of inclusions from the UK group, supporting ample capacity. From 2026, those inclusions are excluded entirely.
Adjusted taxable income accordingly fell to $1.1 million. Therefore, section 163(j) permitted just $330,000 of interest, disallowing $930,000 and deferring roughly $195,000 of tax at 21%. Combined with the British charge, one financing strategy cost the family over £360,000 in a single year.
Planning Around the Corporate Interest Restriction
Several levers genuinely work, provided you pull them before the filing deadline.
Elections Worth Considering
The group ratio election is the obvious starting point. Additionally, the interest allowance non-consolidated investment election and the public infrastructure election suit particular structures. Each requires the reporting company to act within the return.
Model before electing. Furthermore, an election that helps this year can hurt next year, because it binds the period. Consequently, we run multi-year projections rather than optimising a single return in isolation.
Restructuring the Debt Itself
Sometimes the answer is the borrowing rather than the election. For instance, pushing debt into the entity with genuine tax-EBITDA improves capacity under the corporate interest restriction. Similarly, replacing shareholder debt with equity removes interest from the calculation entirely.
Transfer pricing constrains the options. Nevertheless, commercially supportable rates and terms leave real room to manoeuvre. Therefore, debt location deserves review whenever a group refinances.
Modelling Both Regimes Together
The decisive point is coordination. Specifically, a structure optimised purely for the UK fixed ratio can destroy American capacity, and the reverse is equally true. Consequently, single-jurisdiction advice reliably produces a worse answer than joint modelling.
We therefore build one model covering both. Additionally, we test the foreign tax credit outcome under each variant, because a restriction that raises creditable UK tax is not automatically bad. Ultimately, the objective is the lowest combined charge, not the smallest disallowance.
Common Errors We Correct in Client Filings
Five mistakes recur constantly, and each carries a measurable price.
Treating the Threshold as Company-Level
The most expensive error is also the simplest. Specifically, owners assume each company enjoys its own £2 million allowance and conclude that no filing is needed. Consequently, a group with four subsidiaries at £900,000 of interest each believes it sits below the threshold.
The aggregate is £3.6 million. Therefore, the group is squarely inside the corporate interest restriction and has probably missed several returns. Additionally, the elections that would have reduced the charge were never made.
Filing Abbreviated Returns Out of Habit
Abbreviated returns are quicker, so preparers default to them. However, an abbreviated return preserves allowance without claiming reactivation. Consequently, groups carrying disallowed interest from earlier years never recover it, despite having generated the capacity.
The distinction is easy to miss. Furthermore, nothing on the return warns you that relief is being forfeited. Therefore, we review prior periods whenever we inherit a group with historic corporate interest restriction disallowances.
Ignoring the American Side Entirely
British advisers model the UK charge and stop. Meanwhile, American advisers model section 163(j) and stop. Consequently, nobody tests whether a UK election improves or worsens the combined position, and the two answers frequently conflict.
The 2026 change made coordination essential rather than merely desirable. Moreover, a group ratio election that reduces UK tax also reduces creditable foreign tax, which can leave an American owner worse off overall. Therefore, the corporate interest restriction should never be optimised in isolation from the US return.
What the Corporate Interest Restriction Means When You Sell
Exit planning is where trapped interest suddenly acquires a price tag.
Disallowed Amounts Travel With the Company
The attribute is company-specific, which cuts both ways on a sale. Specifically, a share sale carries the disallowed interest across to the buyer, because the company itself is the asset changing hands. Consequently, that balance forms part of what the buyer is acquiring.
An asset sale behaves differently. Meanwhile, selling the properties or the trade out of the company leaves the corporate interest restriction attribute stranded in an entity that will never generate capacity again. Therefore, the deal structure decides whether years of accumulated relief survive.
Why Buyers Diligence Your Interest Returns
Sophisticated purchasers examine these filings closely. Furthermore, they check whether reporting company appointments were valid, whether elections were properly made, and whether returns were filed at all. Gaps translate directly into price adjustments or indemnities.
Unclaimed reactivation is a common finding. Additionally, a seller who never filed full returns cannot credibly value the carried-forward balance. Consequently, tidying the corporate interest restriction history well before a sale process protects real value.
Coordinating the Exit With Your US Return
The American position needs equal attention. Notably, a share sale by an American owner engages its own reporting, and the interaction with your annual US tax return preparation requires planning rather than reaction. Section 163(j) carryforwards at the US holding level do not disappear either.
Sequencing therefore matters. Moreover, accelerating or deferring a completion date across a period end can change both the UK disallowance and the US limitation. Ultimately, we model the exit year in both systems before the sale and purchase agreement is signed.
How TaxYork Can Help
We prepare US and UK filings for investors and company owners running leveraged structures across both systems. Furthermore, we calculate the corporate interest restriction and section 163(j) positions together, then test each planning variant against the combined result.
Our work covers interest restriction returns and reporting company appointments, group ratio and other elections, Form 8990 preparation and carryforward tracking, foreign tax credit modelling, and the Form 5471 reporting that accompanies UK ownership. Additionally, we handle catch-up filings through the IRS Streamlined Filing Compliance Procedures where returns have slipped. Our team follows technical guidance from bodies including the ICAEW Tax Faculty, and we liaise with HMRC directly on group positions.
Above all, we engage before the refinancing rather than after it. Structuring decisions made at the term sheet stage cost a fraction of remediation later. Consider our wider cross-border planning and treaty optimisation support if you hold leveraged UK assets.
Conclusion
The corporate interest restriction denies relief for interest your UK company genuinely paid, and the £2 million de minimis protects far fewer American-owned groups than it once did. Moreover, section 163(j) restricts the same commercial leverage on the American side, and 2026 made that worse by removing CFC inclusions from adjusted taxable income. Consequently, owning a UK company now actively reduces your US interest capacity.
Relief remains available to those who claim it properly. Specifically, disallowed amounts carry forward indefinitely in both systems, while unused UK allowance expires after five years. Therefore, file the returns, make the elections deliberately, and model both regimes as a single problem rather than two.
Contact Us
Speak to a specialist about how the corporate interest restriction and section 163(j) affect your structure. To review your position confidentially, book a consultation with our cross-border team.
Email hello@taxyork.com or call 020 3488 8606.
Disclaimer
This article provides general information only and does not constitute tax advice. Tax rules change, and their application depends on your specific circumstances. Furthermore, no reader should act on the basis of this content alone. Obtain professional advice tailored to your situation. TaxYork accepts no liability for any loss arising from reliance on this material.