Introduction: UK Capital Allowances and the Bill You Did Not Expect
UK capital allowances deliver some of the most generous investment relief in the developed world. However, for an American owner they can quietly manufacture a US tax charge that dwarfs the British saving. Every UK guide on the subject celebrates the deduction. However, none of them mentions what happens when the shareholder holds a blue passport.
The problem is structural rather than accidental. Britain lets you deduct the whole cost of qualifying plant immediately. Meanwhile, America refuses that deduction on foreign assets and then taxes the profit your relief created. Consequently the relief that looks free can cost you six figures.
What UK Capital Allowances Actually Give You
UK capital allowances replace accounting depreciation for tax purposes. Since Britain disallows depreciation in the profit computation, the allowances under the Capital Allowances Act 2001 provide the statutory substitute. Furthermore, they now reach 100% of cost for most new plant and machinery.
HMRC sets out the framework in its capital allowances guidance. Broadly, you claim either an immediate deduction or a percentage of a pooled balance each year. Therefore the timing of relief, not the total amount, drives most planning.
Why Americans Feel the Mismatch
American owners face two tax systems that measure the same profit differently. Britain gives relief now. Conversely, the United States spreads relief over many years and, on foreign assets, spreads it over a longer period still.
At TaxYork we see this collision most often among owners of trading companies, property businesses and professional practices. Notably, the larger the capital programme, the wider the gap becomes.
The 2026 Reforms Reshaping UK Capital Allowances
Three changes to UK capital allowances landed within twelve months, and each one alters the American calculation. Accordingly, any advice written before 2026 is now unreliable.
Full Expensing and the Annual Investment Allowance
Full expensing gives companies a 100% deduction on qualifying new main-rate plant and machinery, with no monetary cap. HMRC explains the conditions in its full expensing guidance. Critically, the asset must be new and unused, so second-hand equipment falls outside.
The annual investment allowance sits alongside it at £1 million per year. Unlike full expensing, it covers second-hand assets and unincorporated businesses. Additionally, groups must share a single allowance between them.
The Writing Down Allowance Cut to 14%
The main pool writing down allowance falls from 18% to 14%. That reduction takes effect from 1 April 2026 for corporation tax and 6 April 2026 for income tax, as HMRC confirms in its policy paper on the new allowance.
Periods straddling that date use a hybrid rate. Specifically, you apportion by reference to the days falling either side. Meanwhile, the special rate pool stays at 6%, and CA23220 records the mechanics.
The New 40% First Year Allowance
A 40% first year allowance arrived for main-rate expenditure incurred from 1 January 2026. Importantly, it carries fewer restrictions than full expensing. Therefore assets bought for leasing qualify, and so does expenditure by unincorporated businesses, per the first year allowances guidance.
The new allowance partially offsets the writing down cut. However, it also creates a genuine choice for American owners, because a 40% claim leaves more profit in the UK charge than a 100% claim does.
Cars, Structures and the Special Rate Pool
Cars sit outside the annual investment allowance entirely, so UK capital allowances on vehicles follow their own rules. Second-hand electric cars and vehicles emitting 50g/km or less enter the main pool, while higher-emitting cars drop into the 6% special rate pool. HMRC covers the detail at CA23535 and in its business cars guidance.
Buildings follow a separate regime. The structures and buildings allowance runs at 3% straight-line. Consequently a fit-out often splits across three different pools, which complicates the American computation considerably.
Why the IRS Ignores Your UK Capital Allowances
Here is the gap on UK capital allowances that no British page addresses. The Internal Revenue Code contains no provision recognising British reliefs. Instead, it applies its own rules to the same assets.
Section 168(g) and the Foreign Use Rule
Section 168(g)(1)(A) requires property used predominantly outside the United States to be depreciated under the alternative depreciation system. ADS uses straight-line recovery over longer class lives. Therefore your London plant depreciates far more slowly for American purposes than for British ones. Publication 946 sets out the classes and conventions.
That single provision drives the entire mismatch with UK capital allowances. Britain may grant 100% in year one. Meanwhile, America may grant well under 10%.
No 100% Bonus Depreciation on British Assets
The One Big Beautiful Bill Act made 100% bonus depreciation permanent for property acquired after 19 January 2025, removing the phase-down that had reached 40%. The IRS summarises the regime in its depreciation and expensing guidance.
American owners of UK assets get none of it. Because section 168(k) excludes property required to use ADS, foreign-use property is ineligible. Consequently the headline American relief simply does not reach your British equipment, and you report the slower figures on Form 4562.
Section 179 and the Taxable Income Ceiling
Section 179 permits immediate expensing up to $2,560,000 for 2026, with the phase-out beginning at $4,090,000 of qualifying purchases. Nevertheless, the deduction cannot exceed your active trade or business income. Additionally, it does nothing for assets held inside a UK company, since the election belongs to the taxpayer conducting the business.
The CFC Trap: When Full Expensing Creates a US Charge
For owners of a UK limited company, UK capital allowances stop being a timing question and become a cash cost. This section matters most.
Tested Income Uses American Depreciation
If your UK company is a controlled foreign corporation, you compute its tested income under US tax principles. Therefore British reliefs are stripped out and ADS depreciation is substituted. The result is a large American profit figure sitting beneath a small British one, reported on Form 5471 and Form 8992.
Net CFC tested income now carries a 40% deduction, producing a 12.6% effective rate for corporate shareholders. Individuals, however, receive no deemed-paid credit at all without an election.
How Relief Drags You Below the High-Tax Threshold
The high-tax exclusion removes an item from the charge when the effective foreign rate exceeds 90% of the US corporate rate, currently 18.9%. Britain's 25% main rate clears that comfortably. Conversely, aggressive UK capital allowances collapse the taxable base, so the tax actually paid falls far below the threshold.
The arithmetic is unforgiving. Full expensing can reduce your effective UK rate to single figures. Consequently the exclusion becomes unavailable, and Regulation 1.951A-2 leaves the income fully within the American charge.
The Section 962 Election
A section 962 election lets an individual shareholder be taxed as though a domestic corporation held the shares. Accordingly you access the 21% rate, the 40% deduction on Form 8993, and a deemed-paid credit at 90% of the foreign tax.
The election carries a cost. Later distributions above the tax already paid become taxable again. Nevertheless, for a well-capitalised trading company the arithmetic usually favours the election decisively.
Sole Traders, Partnerships and the Credit Timing Gap
Unincorporated owners claiming UK capital allowances escape the CFC rules entirely. However, they meet a different problem.
Two Different Deduction Curves
You claim UK capital allowances against UK profit and ADS depreciation against US profit. Because the curves differ, the same business reports a low UK profit and a high US profit in year one. Subsequently the position reverses, as British relief runs out while American relief continues.
That reversal matters enormously. Specifically, it moves foreign tax credits into years when you cannot use them.
Excess Credits Today, Wasted Credits Tomorrow
In the year of heavy investment your UK tax is small, so you generate little credit against a large US liability. Therefore you pay real American tax. Later, when UK relief is exhausted, your UK tax rises and produces credits you no longer need.
Carryovers help but rarely cure the problem. Furthermore, the general basket rules on Form 1116 allow only a one-year carryback and a ten-year carryforward. The IRS explains the framework in its foreign tax credit guidance.
Balancing Charges and Disposals
Selling an asset you claimed UK capital allowances on triggers a balancing charge in Britain and a separate recapture computation in America. Since the two written-down values differ, the gains differ too. Consequently you can face a British balancing charge and an American gain of entirely different sizes in the same year.
Case Study: An American Owner Fitting Out a London Office
Consider Michael, an American who owns a UK trading company outright. During the year to 31 March 2026 the company earns £1,200,000 before allowances and spends £900,000 on new qualifying plant and fit-out.
The British Position
The company claims the most generous UK capital allowances available, taking full expensing on the whole £900,000. Taxable profit therefore falls to £300,000, and corporation tax at 25% comes to £75,000. Michael's accountant reports a saving of £225,000 against the unrelieved position.
Measured against book profit, the effective UK rate is just 6.25%. That number looks like a triumph. However, it is precisely the number that creates the American problem.
The American Position
For tested income the company must use ADS. Assuming a ten-year class life and a half-year convention, first-year American depreciation is roughly £45,000 rather than £900,000. Tested income therefore stands near £1,155,000, or about $1,521,700 at 0.759.
Foreign tax paid is £75,000, roughly $98,800. The effective foreign rate is therefore about 6.5%, far below the 18.9% threshold. Consequently the high-tax exclusion is unavailable and the whole amount enters Michael's return.
What the Election Saves
Without an election, Michael faces ordinary rates up to 37% on approximately $1,521,700, with no deemed-paid credit whatsoever. That produces roughly $563,000 of US tax.
With a section 962 election the position transforms. After the gross-up and the 40% deduction, tax at 21% comes to about $203,000, and the 90% deemed-paid credit of roughly $88,900 reduces it to approximately $114,000. Therefore the election saves close to $449,000.
The Counterintuitive Answer
Now consider the alternative. Had the company claimed only the 14% writing down allowance, UK taxable profit would have been about £1,074,000 and corporation tax roughly £268,500. The effective rate would have exceeded 23%, comfortably above 18.9%, and the high-tax exclusion would have removed the income from the American charge altogether.
The lost British relief is merely deferred, because the expenditure stays in the pool. Ultimately, claiming the most generous UK capital allowances available cost Michael far more in America than it saved in Britain.
Records That Protect Your UK Capital Allowances Claim
Documentation decides whether a claim survives scrutiny in either country. Therefore build the file once and use it twice.
Keep the Asset Register on Two Bases
Maintain one register showing British pools alongside American classes. Each asset needs its cost, its acquisition date, the UK capital allowances claimed, and the ADS life applied for US purposes. Furthermore, record the exchange rate used and the date it relates to.
That discipline pays for itself at disposal. Because the two written-down values diverge from year one, reconstructing them years later is expensive and often impossible.
Reconcile Pools to the US Computation Annually
Review the reconciliation every year rather than at sale. Specifically, confirm that the pool balances still tie back to your American basis schedules. Additionally, check whether any asset moved between the main pool and the special rate pool.
Movements matter more than owners expect. A reclassification changes the British relief profile, so it also changes the effective foreign rate that determines your exposure.
Evidence the Effective Rate Before You File
Compute the effective foreign tax rate under each available claim before the UK return goes in. Consequently you can still choose a smaller claim if the larger one destroys the exclusion. Once the return is filed, that option narrows considerably.
Retain the workings alongside the return. Where UK capital allowances shaped the American outcome, the IRS will want to see how you arrived at the figures, and Publication 946 sets the expectation for substantiation.
How TaxYork Can Help
We prepare US and UK returns for company owners, investors and professional practices claiming UK capital allowances across both systems. Consequently we model the allowance decision before the UK return is filed, not afterwards.
Our work begins by rebuilding the asset register on both bases. Furthermore, we test the effective foreign rate against the high-tax threshold under each claim scenario. Where an election helps, we quantify it and prepare the supporting statements.
We also review prior years. Where earlier claims created an unreported inclusion, catching up on missed US tax returns is usually straightforward while the position remains non-wilful. Guidance from the ICAEW technical tax faculty and the AICPA tax resources informs our approach. Similarly, our foreign tax credit and treaty work addresses the credit timing gap directly.
Conclusion
UK capital allowances reward investment generously, and Britain has made them more generous still for 2026. Full expensing delivers 100%, the annual investment allowance covers £1 million, and a new 40% first year allowance now sits beside a reduced 14% writing down rate.
American owners cannot simply accept the largest claim available. Because section 168(g) forces slow ADS depreciation on foreign assets, the United States measures a much higher profit. Therefore an aggressive British claim can strip out the high-tax exclusion and pull the entire profit into the American charge.
Above all, treat the allowance decision as a two-country calculation. Model the effective foreign rate before you file, consider whether a smaller claim preserves the exclusion, and price the election properly. Ultimately, the right answer depends on both returns, never on one.
Contact Us
Speak to our specialists before you finalise your next capital allowances claim. You can contact us or book a consultation at a convenient time.
Email hello@taxyork.com or telephone 020 3488 8606. Additionally, you can explore our cross-border tax planning for business owners and our US tax return preparation for expats. Current rates appear in the rates and pools guidance and in Finance Act 2026.
Disclaimer
This article provides general information about UK capital allowances and their United States tax consequences. It does not constitute tax advice for any particular person or situation. Tax legislation, rates and thresholds change frequently, and the application of any rule depends on individual circumstances. Therefore you should obtain professional advice before acting on anything set out here. TaxYork accepts no liability for loss arising from reliance on this article without such advice.