Corporation Tax Marginal Relief for Property Companies: The Associated-Company Squeeze

The headline corporation tax position for a UK property company looks simple: 19% on the first £50,000 of profit, 25% above £250,000, marginal relief in between. The associated-companies rule makes the position considerably more complicated for the average portfolio landlord, because almost every BTL portfolio that runs through more than one SPV has its bands divided by the number of associated companies. A five-company structure (one HoldCo and four SPVs) reduces the £50,000 small-profits-rate band to £10,000 per company and pushes any SPV with more than £50,000 of profit straight into the 25% main rate.

This page works through the formula, the associated-companies arithmetic, the augmented-profits adjustment for franked investment income, the close investment-holding company carve-out that excludes connected-party letting from the small profits rate altogether, and worked examples for standalone and multi-SPV structures. For the underlying corporation tax rates and bands, see our corporation tax rates for property companies 2026/27 guide. For the parallel question of moving losses around the group, see our corporation tax group relief guide.

What marginal relief does

Marginal relief in part 3A of the Corporation Tax Act 2010 exists to soften the transition between the 19% small profits rate and the 25% main rate. Without it, a company with £49,999 of profit would pay £9,500 of corporation tax (19%) while a company with £50,001 of profit would pay £12,500 (25%), a £3,000 jump for £2 of extra profit. The relief smooths the transition by applying the main rate to the whole profit and then granting a tapered deduction that effectively phases in the 25% rate between the lower and upper limits.

The lower limit is £50,000 and the upper limit is £250,000. Between those two figures, an additional £1 of profit costs an extra 26.5p of corporation tax (the so-called effective marginal rate). The figure is 25p at the main rate plus 1.5p of marginal relief withdrawal. Beyond £250,000 the relief is exhausted, the main rate applies to the whole profit, and the effective rate settles back to 25%.

For a single property SPV with arm's-length tenants and no other associated companies, the bands operate as headline-stated. The squeeze comes from associated companies.

The associated-companies rule

Two companies are associated under section 18E CTA 2010 if one controls the other, or both are controlled by the same person or group of persons. The associated-companies count for an accounting period is the number of companies that are associated at any time during the period (plus the company itself).

The £50,000 and £250,000 thresholds are divided by the associated-companies count. The arithmetic is unforgiving for portfolio landlords running an SPV-per-property model:

• One company alone: lower £50,000, upper £250,000.
• Two associated companies (HoldCo + one SPV): lower £25,000, upper £125,000.
• Three: lower £16,667, upper £83,333.
• Five (HoldCo + four SPVs): lower £10,000, upper £50,000. The marginal-relief band has collapsed to a single point at £50,000 of profit; any profit above £10,000 is taxed at the main rate effectively.
• Ten: lower £5,000, upper £25,000.

Two narrow carve-outs from the associated-companies count exist in section 18L CTA 2010. Dormant companies (no taxable activity in the period) are excluded. Passive holding companies that exist solely to hold shares in subsidiaries, with no other income or activity, are also excluded under the so-called passive holding company exemption. Both exclusions are narrow; HMRC reads the conditions strictly. A holding company with even modest bank interest income usually falls outside the passive holding company exemption.

The marginal relief formula

The statutory formula in section 18N CTA 2010 is straightforward but the variable names get in the way. In plain English:

• Calculate corporation tax on taxable total profits at the main rate of 25%.
• Subtract marginal relief calculated as: (upper limit minus augmented profits) × (taxable total profits ÷ augmented profits) × 3/200.

The result is the corporation tax payable. The variables:

• Taxable total profits: the profits that are actually subject to corporation tax (after deductions, before chargeable gains adjustments).
• Augmented profits: taxable total profits plus exempt distributions received from non-group companies. For most property SPVs this equals taxable total profits because the SPV does not receive dividends from outside its group.
• Upper limit: £250,000 divided by the number of associated companies, pro-rated for a short accounting period.
• 3/200: the marginal relief fraction, equivalent to 1.5%.

The mathematical effect is the 26.5% effective marginal rate between the lower and upper limits. Inside that band, every additional £1 of profit adds £0.265 to the corporation tax bill (£0.25 at the main rate plus £0.015 of withdrawn marginal relief).

Worked example: standalone SPV with £100,000 of profit

Single residential BTL SPV, arm's-length tenants, no associated companies, no franked investment income. Taxable total profits: £100,000.

• Main rate corporation tax: £100,000 × 25% = £25,000.
• Marginal relief: (£250,000 − £100,000) × (£100,000 ÷ £100,000) × 3/200 = £150,000 × 1 × 0.015 = £2,250.
• Corporation tax payable: £25,000 − £2,250 = £22,750.
• Effective rate: 22.75%.

Cross-check using tiered rates: 19% on first £50,000 = £9,500; 26.5% on the next £50,000 = £13,250; total £22,750. The two methods give the same answer because the formula is constructed to deliver exactly the 26.5% marginal rate in the band.

Worked example: five-company portfolio with £100,000 per SPV

Same setup but the landlord runs a HoldCo with four SPV subsidiaries. All five companies are active in the accounting period; none is dormant. Each SPV has taxable profits of £100,000. Five associated companies.

Per-SPV thresholds:

• Lower limit: £50,000 ÷ 5 = £10,000.
• Upper limit: £250,000 ÷ 5 = £50,000.

Each SPV's profits of £100,000 exceed the upper limit of £50,000, so no marginal relief is available. The main rate of 25% applies to the whole £100,000.

• Corporation tax per SPV: £100,000 × 25% = £25,000.
• Across four SPVs: £100,000 of corporation tax.
• HoldCo: passive holding company exemption applies if it has no income; otherwise own corporation tax position calculated on its own profits.

Comparison to four standalone SPVs (one each, no associated companies): each SPV's £100,000 of profit attracts £22,750 of tax (the standalone calculation from the previous section). Total tax across four independent SPVs: £91,000. The associated-companies penalty is £9,000 per year, recurring as long as the structure is in place.

The same group of properties consolidated into a single company with £400,000 of total profit would pay 25% on the whole amount: £100,000. Identical to the five-company group result. The associated-companies penalty exists to prevent fragmentation that would otherwise capture multiple small-profits-rate bands; once profits across a controlled group exceed the (consolidated) upper limit, the relief disappears regardless of corporate structure.

Close investment-holding companies: the connected-party let trap

A separate disqualification removes some property companies from the small profits rate and marginal relief entirely. Under section 18N CTA 2010, a close investment-holding company (CIHC) pays the main rate of 25% on all profits with no access to the small profits rate or marginal relief.

A close company is a CIHC for an accounting period unless it exists wholly or mainly for one or more of the qualifying purposes. The most-relevant qualifying purposes for property companies are:

• Carrying on a trade or trades on a commercial basis.
• Making investments in land where the land is, or is intended to be, let to persons other than persons connected with the relevant company.
• Holding shares in or making loans to other group members that themselves satisfy a qualifying purpose.

The land-letting carve-out is the critical one for BTL landlords. A property company that lets to unconnected tenants is not a CIHC. A property company that lets to a connected person (a director's spouse, the director themselves, or any other person connected under section 1122 CTA 2010) is at risk of CIHC status if the connected-party letting is the main activity.

The mixed-let case is the boundary. A company that lets four properties to unconnected tenants and one to the director's adult child is unlikely to be a CIHC because the connected-party letting is not the main activity. A company that lets one property to the director and one to unconnected tenants is borderline. A single-property SPV letting to the director's spouse is almost certainly a CIHC.

The CIHC test is applied for each accounting period. A change in letting arrangements mid-year (the property is let to a connected person for six months then to unconnected tenants for six months) requires a judgement call on whether the connected-party use was the main activity for the period as a whole.

Planning around the associated-companies rule

The structural responses to the associated-companies squeeze fall into three groups.

Don't fragment when it doesn't add value. The SPV-per-property model is genuinely useful where each property has a different lender, different shareholders, or a clear ring-fencing reason. Where the rationale is purely "we always do it that way", consolidating into fewer larger companies usually delivers a tax saving plus accounting and administration savings. The question to ask at each new acquisition is whether a separate SPV adds value over adding the property to an existing one.

Manage profit levels per SPV. Where the structure has to be five SPVs for non-tax reasons, marginal relief can still be captured by keeping individual SPV profits at or below the divided lower limit. Pension contributions, R&D where genuinely applicable, capital allowances on commercial property elements, and the timing of refurbishment expenditure can all bring an SPV's profits below the £10,000 (or £8,333, or £5,000) lower limit and restore access to the 19% small profits rate.

Use the dormant-company exclusion deliberately. A genuinely dormant company is excluded from the associated-companies count. Where a portfolio includes legacy companies that no longer trade or invest, formally dormant-ifying them at Companies House and ensuring no taxable activity passes through them protects the divisor for the active SPVs. The Companies House DS01 strike-off is an alternative for companies that will never be used again.

None of these responses is dramatic on its own; the saving comes from getting the structure right at the point of each new SPV decision rather than from a one-off restructure.

Five failure modes we see on portfolio reviews

The recurring errors when we review historical corporation tax positions for portfolio landlords are mechanical rather than complex. Each is fixable once spotted.

Dormant exclusion misapplied. A company is dormant under section 18L only if it has no taxable activity at all in the accounting period. A small amount of bank interest, a cancelled-but-not-fully-cleared trade, or a residual rental income on a property in run-off all break the dormant status. We routinely see landlords with three "dormant" companies in a portfolio, only one of which actually qualifies.

Associated-companies count missed entirely. Where a portfolio has grown organically and each SPV has been filing its own CT600 with its own accountant, the associated-companies count is sometimes never recalculated. Each SPV files on the basis of the full £50,000 / £250,000 thresholds. HMRC's compliance work in the 2024 and 2025 cycles has picked up several cases of this and amended back returns. The amendments come with late-payment interest.

Passive holding company exemption claimed too generously. The passive holding company exemption in section 18L requires the company to have no income at all other than dividends from its subsidiaries (in narrow circumstances). A holding company that charges a management fee to its subsidiaries, receives interest on inter-company loans, or holds any cash earning bank interest does not qualify. The exemption is much narrower than landlords usually assume.

CIHC status overlooked on connected-party lets. Where a single-property SPV lets to the director's child or spouse during a transition (between tenants, while a renovation is underway, as a temporary family housing solution), CIHC status often applies for that accounting period. The company should be filing as a CIHC, paying 25% on all profits with no marginal relief. The mistake costs 6 to 7 percentage points of tax on profits in the £10,000 to £50,000 band.

Marginal relief calculation done on the wrong augmented profits. Where a holding company receives a dividend from a JV company it is not in a 51% group with, the dividend counts toward augmented profits. The marginal relief is reduced because the formula compares the upper limit against augmented profits, not taxable profits. We see this overlooked on holding companies that take small dividend slices from joint-venture developments.

Where marginal relief sits in the wider tax picture

Marginal relief is one of three corporation-tax-rate planning levers available to a property group. The others are CIHC avoidance (don't let to connected persons if the small profits rate matters) and group relief for losses (don't let losses sit unused in one SPV when another has profits to extinguish).

For a single-company landlord with profits comfortably above £250,000, marginal relief is irrelevant because the main rate applies anyway. For a single-company landlord with profits comfortably below £50,000, the small profits rate applies and there is nothing to lose from associated-companies analysis. The companies most affected by the rules are mid-range portfolio landlords with three to seven SPVs each generating £40,000 to £80,000 of profit; this is exactly the band where the associated-companies divisor turns the small-profits-rate band into a small-profits-rate point.

For the related question of how to extract cash from these companies efficiently, see our director's loan account mechanics guide. For how losses move between SPVs to extinguish profits and reduce the marginal-relief problem, see our corporation tax group relief guide.