Section 24: Mortgage Interest Restriction for Landlords

Section 24 of the Finance (No. 2) Act 2015 fundamentally altered the economic model for individual buy-to-let (BTL) investors across the UK. By permanently eliminating a landlord’s historic right to treat residential mortgage interest as a standard business expense, the legislation forces property owners to calculate their income tax liabilities using an entirely different accounting sequence.

1. The Operational Shift: From Full Deduction to a 20% Tax Credit

Prior to the rollout of Section 24, individual landlords operated on a "net profit" model. They simply subtracted 100% of their mortgage interest and finance costs from their gross rental income, paying income tax only on the leftover profit margin.

Under the fully phased-in modern framework, finance costs are completely disallowed as an expense deduction. Instead, the tax code implements a multi-step calculation process:

1. Gross Profit Assessment: You pay income tax on your full rental revenue after deducting only non-finance allowable expenses (such as letting agent fees, landlord insurance, and direct property maintenance).
2. Marginal Rate Application: This expanded gross profit figure is taxed at your standard personal marginal rate (20%, 40%, or 45%).
3. The Tax Credit Reduction: After your baseline tax bill is calculated, HMRC applies a flat 20% basic rate tax credit based on your total qualifying finance costs. This credit is subtracted directly from your final tax bill.

The 2027 Property Tax Rate Adjustment: While the tax credit is currently pegged to the standard 20% basic rate, upcoming legislative changes will alter this baseline. Starting on 6 April 2027, the government is introducing separate, dedicated tax bands for income derived specifically from property (22% basic, 42% higher, and 47% additional rate). In alignment with this shift, the Section 24 finance cost relief credit will scale up to 22% from April 2027 onward to match the new property basic rate.

2. Who Falls Under the Scope of Section 24?

The structural exposure of Section 24 depends entirely on the legal structure holding the underlying property deeds:

Exposed Entities

• Individual property owners holding residential buy-to-let titles in their personal names.
• Individual partners operating within traditional unincorporated property partnerships.
• Furnished Holiday Lettings (FHLs): Following the complete statutory abolition of the specialized FHL tax regime, short-term holiday lets no longer enjoy automatic exemption. Individual holiday let owners are now fully exposed to the standard Section 24 20% tax credit restrictions.

Exempt Entities

• Limited Companies: Corporate structures are entirely exempt from Section 24. A limited company can still treat 100% of its mortgage interest as a standard, fully deductible business expense before its profits face Corporation Tax.
• Commercial Real Estate: Properties utilized for commercial purposes (such as retail shops, warehouses, or offices) remain outside the scope of Section 24, regardless of individual ownership.

3. The Three-Part Statutory Reduction Cap

The 20% tax credit is not automatically guaranteed on every pound of interest you pay. Under statutory rules, the credit is explicitly limited to the lowest of three specific operational parameters:

• Parameter 1: 20% of your actual qualifying property finance costs paid during the tax year (including mortgage interest, amortized arrangement fees, and loan interest for capital enhancements).
• Parameter 2: 20% of your property business net profits after subtracting all other allowable operational expenses.
• Parameter 3: 20% of your "adjusted total income"—meaning your entire global taxable income from all sources (excluding savings and dividends) that clears your standard UK Personal Allowance.

If parameter 2 or 3 scales lower than your actual mortgage spending—for instance, if your property business records an overall net trading loss after a major roof repair—the excess unrelieved tax credit is not destroyed. Instead, it is automatically carried forward to be applied against your property tax liabilities in subsequent tax years.

4. The Basic Rate "Bracket Creep" Trap

The most dangerous financial element of Section 24 is how it artificially inflates a landlord's taxable income, forcing basic rate taxpayers into higher tax brackets without their realizing it.

Because mortgage interest can no longer be deducted at step one, your "taxable profit" appears significantly larger on paper.

The Bracket Creep Mechanism:

An individual earns a regular salary of £40,000 from their primary employment. They own a BTL property generating £15,000 in rent, facing £7,000 in mortgage interest and £1,000 in maintenance costs.

• The Old System View: Their taxable rental profit was £7,000 ($£15,000 - £7,000 - £1,000$). Added to their salary, their total income sat at £47,000, safely inside the basic rate bracket (£50,270 limit).
• The Section 24 Reality: Their taxable rental profit jumps to £14,000 because the mortgage interest is ignored during initial parsing ($£15,000 - £1,000$). Added to their salary, their total income appears as £54,000.
• The Bracket Breach: This calculation pushes £3,730 of their income into the 40% Higher Rate tax band ($£54,000 - £50,270$). While the 20% tax credit helps offset the final bill, the artificial income inflation can trigger secondary financial penalties, such as phasing out Child Benefit or reducing student loan repayment thresholds.

Key Points to Remember

• Section 24 bans individual landlords from deducting mortgage interest from gross rental profits.
• Relief is restricted to a flat 20% tax credit, which will update to a 22% credit in April 2027.
• Limited companies are exempt, retaining the right to deduct 100% of finance costs from revenue.
• The 20% credit is strictly capped at the lowest of your interest costs, net rental profits, or adjusted net income.
• Unused credits resulting from property losses can be safely carried forward to future tax years.
• Gross profit calculations can artificially boost your income profile, pulling basic rate taxpayers into the 40% tax tier.