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    TaxKilnUK tax guidance
    TaxKilnUK tax guidance

    Section 24, Mortgage Interest Restriction

    TaxKiln framework

    Section 24 Step-Down Method

    TaxKiln's analytical method for modelling Finance (No.2) Act 2015 s.24 interest restriction — applying basic-rate tax credit recovery against higher-rate-band liability for residential landlords, where the relief actually evaporates for portfolio landlords.

    The TaxKiln Section 24 Step-Down Method models the basic-rate tax credit not as a flat 20% deduction but as a step-down against higher-rate-band liability, because that is where the relief actually evaporates for portfolio landlords with mortgage interest pushing them across the higher-rate threshold.

    Section 24 restricts individual residential landlords' ability to deduct mortgage interest + other finance costs from rental income. Fully in effect since 6 April 2020 (phased in from April 2017). Mechanic: finance costs (loan interest, arrangement fees, interest on improvement loans, early repayment charges) are NOT deductible as a rental expense. Instead, landlords receive a 20% BASIC-RATE TAX CREDIT calculated on the LOWER of: (a) finance costs paid in the tax year; (b) property profits before deducting finance costs; (c) total income above the personal allowance. Higher-rate (40%) landlords previously received 40p relief per £1 of mortgage interest; under Section 24 they receive only 20p, a 50% reduction in effective relief. Additional-rate (45%) landlords move from 45p to 20p per £1. **Critical scope**: Section 24 applies ONLY to individual landlords holding RESIDENTIAL property in personal names. LTD COMPANIES are entirely unaffected, they continue to deduct mortgage interest fully as a business expense. Commercial property is also outside scope. From April 2027 (Autumn Budget 2025): property income outside Scotland will be subject to SEPARATE income tax rates (22% / 42% / 47%) with finance cost relief at the 22% basic property rate, a further effective restriction.

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    Guidance, not advice. We explain the rules, we don't assess your situation. Always seek financial or tax advice from your accountant, or contact HMRC. Read our editorial scope →

    What this relief is, in plain English

    Section 24 is the single most consequential UK tax reform affecting buy-to-let landlords in the last 20 years. The mechanic, restricting mortgage interest deductibility for individual residential landlords, fundamentally changed the after-tax economics of UK private residential investment. Pre-2017 a higher-rate landlord earning £30,000 rental income + paying £20,000 mortgage interest had taxable profit £10,000 + paid £4,000 tax. Post-Section 24 the same scenario taxes the full £30,000 rental income + gives only 20% basic-rate credit on the £20,000 interest = effective tax £12,000 - £4,000 = £8,000. The £4,000 extra annual tax represents a structural erosion of net rental yield, often turning previously profitable buy-to-let arrangements into break-even or loss-making positions for higher-rate landlords with significant mortgages. The scope is narrow but heavily impactful. Section 24 applies ONLY to INDIVIDUAL landlords (sole, joint, partnership) holding RESIDENTIAL property in personal names. Limited Companies are entirely outside scope, they deduct mortgage interest as a normal business expense. Commercial property is outside scope. From April 2025, former Furnished Holiday Let properties became subject to Section 24 (they were previously outside it). The Limited Company exemption has driven a structural shift in UK landlord behaviour: new buy-to-let acquisitions are increasingly via Ltd Co; existing portfolios are sometimes transferred to Ltd Co (subject to SDLT + CGT on the transfer); the residential property investment industry has built sophisticated structures around the Section 24 / corporate-landlord divide. From April 2027 the reform deepens: property income will have its own separate income tax rates (22% / 42% / 47% in England, Wales, Northern Ireland), with finance cost relief at the 22% basic property rate. The combined effect of Section 24 + separate rates is to make individually-held residential property investment increasingly tax-disadvantaged versus corporate-held or non-property investment.

    How it works

    20% basic-rate tax credit on lower of three amounts

    Finance costs (mortgage interest, loan arrangement fees, interest on improvement loans, early repayment charges) are NOT deductible from rental income. Instead, a 20% tax credit applies to the LOWER of: (a) finance costs paid in the tax year; (b) property profits before deducting finance costs; (c) total income above the personal allowance. The three-test mechanic prevents the credit being claimed when there's no income to relieve it against. Excess finance costs (where capped by tests b or c) can be CARRIED FORWARD to future tax years against the same property business.

    Effective rate impact varies by taxpayer band

    **Basic-rate (20%) landlord**: previously deducted interest at 20% → now gets 20% credit → NO CHANGE in effective relief. **Higher-rate (40%) landlord**: previously deducted at 40% → now gets 20% credit → 50% REDUCTION in effective relief value. **Additional-rate (45%) landlord**: previously deducted at 45% → now gets 20% credit → ~56% REDUCTION. The reform was specifically targeted at higher-rate-taxpayer landlords with significant mortgages, the population structure of UK private residential investment changed substantially as a result over 2017-2025.

    Scope: individual residential landlords only

    Section 24 applies to: individual landlords (sole or joint owners) holding RESIDENTIAL property in personal names; partnership landlords; trustees holding residential property; UK trust structures. NOT in scope: Ltd Cos (full mortgage interest deduction continues); commercial property of any kind; furnished holiday lets PRE-April 2025 (now in scope post-April 2025); rooms-in-main-home let under Rent-a-Room (different scheme entirely). The Ltd Co exemption has driven incorporation-restructuring among substantial individual landlord portfolios, subject to SDLT + CGT on the transfer.

    April 2027 reform, separate property income tax rates

    Autumn Budget 2025 announced separate property income tax rates from 6 April 2027 (outside Scotland, devolved): 22% basic / 42% higher / 47% additional. These rates apply ONLY to property income, not other income. Finance cost relief under Section 24 from April 2027 will be at 22% (the separate property basic rate), slight increase in credit value but more than offset by increased headline rates. Combined effect: net additional tax cost for most landlords. Scottish position devolved + handled separately by Scottish Parliament. Transitional rules being finalised through 2026.

    Who qualifies

    Interactions with other reliefs

    FHL Abolition (from 6 April 2025)

    Former FHL properties were OUTSIDE Section 24 (full mortgage interest deduction). From 6 April 2025 FHL abolition brings them INTO Section 24, restricting interest deduction to 20% basic-rate credit. The combined impact on a former FHL landlord: loss of BADR at disposal (10%/14% → 24%) + loss of capital allowances on furniture (replaced by Replacement of Domestic Items relief) + Section 24 now restricting interest. Often makes short-let holiday properties no longer viable as private-individual investments.

    Ltd Co buy-to-let structure

    Ltd Cos are EXEMPT from Section 24, fully deduct mortgage interest as business expense. Many higher-rate landlords have moved (or are considering moving) properties from personal names to Ltd Co structure. Trade-offs: incorporation triggers SDLT + CGT on transfer; ongoing CT (19-25%) + dividend tax on extraction vs personal income tax (40-45%); s.162 TCGA 1992 incorporation relief can defer CGT but not eliminate it. Specialist advice essential, incorporation is rarely worthwhile for single-property portfolios but often worthwhile for substantial holdings with long-term outlook.

    Property Allowance (£1,000)

    If gross property income is below £1,000, Property Allowance gives full relief + Section 24 mechanics are irrelevant (no taxable property income to relieve). Above £1,000, the landlord can elect Property Allowance (£1k deduction, ignore actual costs) OR claim actual expenses (then Section 24 applies on finance costs). Most mortgaged buy-to-let properties have far above £1,000 of relevant costs so actual expenses route is used + Section 24 then bites.

    Replacement of Domestic Items Relief

    Replacing furniture, white goods, carpets, curtains in furnished residential lettings remains deductible. Section 24 doesn't restrict these, they're not finance costs. Combined with Section 24's interest restriction, landlords often find Replacement of Domestic Items is one of the few remaining valuable deductions for residential letting. Property allowance (£1k) + Replacement of Domestic Items + Section 24 credit are the three reliefs to plan together for most individual residential landlords.

    Common mistakes + audit triggers

    Worked example

    Patricia, Bristol - Higher-rate-taxpayer individual landlord with 3 buy-to-let properties + significant mortgage interest (2025/26)

    Patricia owns 3 buy-to-let flats in Bristol, all in her personal name. 2025/26 totals: gross rental income £42,000; allowable expenses (letting agent, insurance, maintenance, repairs) £8,000; mortgage interest paid £18,000. She's also a higher-rate-taxpayer through her PAYE employment (£75,000 salary). Her partner doesn't earn enough to use Marriage Allowance.

    Calculation: **Step 1: Compute pre-Section-24 property profit (illustrative only).** If mortgage interest were deductible (Ltd Co scenario): - Gross rent £42,000 - Allowable expenses £8,000 - Mortgage interest £18,000 = Taxable profit £16,000 - Tax at higher rate 40%: £6,400 **Step 2: Compute post-Section-24 actual position (individual landlord).** Property profit for tax purposes: - Gross rent £42,000 - Allowable expenses £8,000 = Property profit BEFORE finance costs £34,000 - (Mortgage interest NOT deducted) - Property profit subject to income tax: **£34,000** This £34,000 stacks on top of her £75,000 PAYE → total income £109,000 (all higher-rate band, partial additional-rate band, also breaches £100k PA-taper trigger). Tax on £34,000 of property income at higher rate 40%: £13,600. **Step 3: Section 24 finance cost tax credit calculation.** Credit = 20% × lower of: (a) Finance costs paid £18,000 (b) Property profits before finance costs £34,000 (c) Total income above PA £109,000 - £12,570 = £96,430 Lower of (a), (b), (c) = £18,000 (finance costs). Tax credit: 20% × £18,000 = **£3,600**. **Step 4: Effective tax on property activity.** Tax on property income: £13,600 Less Section 24 credit: -£3,600 **Effective property tax: £10,000** **Step 5: Comparison.** If Section 24 didn't apply (Ltd Co): £6,400 tax on £16,000 profit. Actual Section 24 outcome: £10,000 effective tax. **Additional annual tax from Section 24: £3,600 (£10,000 - £6,400 + adjustment for PA taper not modelled).** Plus Patricia's adjusted net income £109,000 triggers PA taper: £4,500 PA reduced × 40% = £1,800 additional tax via PA loss. **Total annual Section-24-driven cost: ~£3,600 + £1,800 PA-taper cascade = £5,400/year.** **Step 6: Strategic options.** A) **Status quo**: accept £5,400/year additional tax. Net property profit (after all tax + finance costs): £42,000 - £8,000 - £18,000 - £10,000 = £6,000/year. Yield calculation: depends on property values. B) **Incorporate**: transfer 3 properties to a Ltd Co. SDLT cost (3% surcharge on residential value): assume properties worth £900,000 combined = SDLT £58,500 (5% × £675k + 3% surcharge × £900k roughly). CGT on transfer: assume gains £200,000 combined = £48,000 at 24%. Total one-off cost: £106,500. Annual savings ~£5,400. Break-even: ~20 years. Likely not worthwhile unless very long-term hold + portfolio growth planned. C) **Sell-down**: dispose of most-mortgaged property to reduce overall finance costs. Reduces Section 24 exposure but realises CGT. Worth modeling property-by-property. D) **Pension contributions**: £20,000 net pension contribution → £25,000 gross → adjusted net income reduces by £25,000 → drops below £100k PA-taper trigger → recovers full PA (£1,800 saving). Pension tax relief 40% × £25,000 = £10,000. Combined relief: £10,000 + £1,800 PA recovery = £11,800. Far higher ROI than the structural incorporation option. THIS IS THE OPTIMAL INTERVENTION for Patricia at this scale. **Practical conclusion**: At this portfolio size, Patricia should focus on pension contributions to bring adjusted net income below £100k + accept Section 24's additional tax cost on the property activity itself. Incorporation rarely makes sense for 3-property portfolios unless growth + 20+ year hold are planned.

    Statute reference: Finance (No. 2) Act 2015 + Income Tax (Trading and Other Income) Act 2005 FA(No.2) 2015 Part 4 + ITTOIA 2005 s.272A. HMRC manual: PIM2050 onwards.

    Frequently asked questions

    What happens if I miss the Self Assessment deadline?+
    The Self Assessment deadline is 31 January (online filing) for the previous tax year. Miss it and HMRC apply an automatic £100 penalty. Beyond that: £10 per day from 3 months late (capped at £900), 5% of tax due at 6 months late, and another 5% at 12 months late, under Schedule 55 of the Taxes Management Act 1970. If you have a genuine reason (serious illness, bereavement, technical issue with HMRC's systems) you can appeal with evidence; HMRC accepts reasonable excuse appeals in most genuine cases.
    Do I need an accountant or can I file Self Assessment myself?+
    Legally you can file Self Assessment yourself via gov.uk for free, most simple sole-trader returns (single income source, basic expenses) are realistic to self-file. An accountant adds real value when: your trading profit is above £40,000 (extraction-strategy decisions matter), you have multiple income streams (PAYE + self-employment + property + dividends), you've crossed the £90,000 VAT threshold, you're considering incorporation, or you have an HMRC enquiry. Expect to pay £400-£1,500/year for a typical sole-trader accountant; the cost is itself a deductible expense.
    How do payments on account work?+
    When your Self Assessment tax bill exceeds £1,000 for the first time, HMRC requires payments on account toward NEXT year's tax. Half the current bill is due 31 January (alongside the current bill); the other half is due 31 July. So your first January after crossing the threshold can hit with a double-bill: last year's balance + first payment on account. Adjust via Form SA303 if you expect next year's income to drop substantially. Payments on account don't apply if more than 80% of your tax is collected via PAYE.
    I'm a higher-rate-taxpayer landlord with £20,000 mortgage interest on my buy-to-let, how much extra tax do I pay under Section 24?+
    Pre-Section 24 position (theoretical): £20,000 interest deducted from rental income → at 40% higher rate, this would save you £8,000 in tax (40% × £20,000). Post-Section 24 position: £20,000 interest gets only a 20% basic-rate tax credit → saves you £4,000 (20% × £20,000). **Additional tax cost from Section 24: £4,000/year per £20,000 of mortgage interest**. For a portfolio with £100,000 of annual mortgage interest, the cost is £20,000/year extra tax for a higher-rate landlord, a significant ongoing erosion of net rental yield. Many higher-rate-taxpayer landlords have responded by: (a) transferring properties to Ltd Cos (subject to SDLT + CGT on transfer); (b) restructuring as company landlords for new acquisitions; (c) accepting the higher tax cost on existing portfolio + adjusting investment thesis; (d) selling down + redeploying capital.
    Should I incorporate my buy-to-let portfolio to escape Section 24?+
    It depends, incorporation has significant upfront tax costs that often exceed the Section 24 savings. **One-off costs of transferring properties to Ltd Co**: SDLT on full market value of properties transferred (3% surcharge on residential properties); CGT on the difference between current market value + original cost (24% residential rate for higher earners); legal + structural costs; potentially mortgage re-financing if existing lender doesn't lend to Ltd Co. **Ongoing benefits**: Ltd Co deducts mortgage interest in full → no Section 24 restriction; CT at 19-25% vs personal IT at 40-45%; profits accumulate in Ltd Co without immediate personal tax. **Break-even analysis**: typically takes 8-15 years for the ongoing tax savings to exceed the one-off SDLT + CGT incorporation cost. Worth incorporating if: long-term landlord intent (10+ years); building a substantial portfolio (5+ properties); planning to leave rental profits in the company. Not worth it if: short-term holding; small portfolio (1-2 properties); planning to extract all rental income as personal cash flow. Specialist tax + legal advice essential, incorporation relief (s.162 TCGA 1992) can defer the CGT but doesn't eliminate it.
    Does Section 24 apply to former FHL properties from April 2025?+
    Yes, this is one of the most punitive aspects of the FHL abolition from 6 April 2025. Properties that were FHLs (qualifying short-let furnished holiday properties) previously enjoyed FULL mortgage interest deduction as a business expense, outside Section 24. From 6 April 2025, former FHL properties are treated as ORDINARY RESIDENTIAL RENTAL income → Section 24 applies → mortgage interest restricted to 20% basic-rate credit. Combined with the loss of BADR (10%/14% CGT on disposal under FHL → standard 24% residential rate now) + loss of capital allowances on furniture, the FHL abolition has dramatically reduced the after-tax economics of short-let holiday property investment. Many ex-FHL owners are reviewing whether continued holiday-letting makes economic sense vs longer-term residential lets (similar tax position) vs sale + redeployment.
    What's the April 2027 change to property income tax rates?+
    Autumn Budget 2025 announced that property income (outside Scotland) will be subject to SEPARATE income tax rates from 6 April 2027: 22% basic rate (vs current 20%); 42% higher rate (vs current 40%); 47% additional rate (vs current 45%). These rates ONLY apply to property income, not to other taxable income. Finance cost relief under Section 24 from April 2027 will be given at the SEPARATE PROPERTY BASIC RATE of 22% (vs current 20%), a small increase in relief value but more than offset by the increased headline rates on property income. NET effect for most higher-rate landlords: tax on property income increases. The reform is part of Treasury's broader effort to make property rental investment less tax-favoured relative to other income types + drive policy outcomes around housing supply + market structure. Specific transitional rules + Scottish position (devolved income tax) are still being finalised, track HMRC guidance through 2026 for implementation detail.

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