The Section 24 tax credit 20% system fundamentally changed how landlords claim mortgage interest relief. Instead of deducting mortgage interest from rental income before calculating tax, landlords now receive a tax credit worth 20% of their mortgage interest payments.
This shift from full deduction to basic rate relief has significantly increased tax bills for higher and additional rate taxpayers. Understanding exactly how this 20% tax credit works is crucial for calculating your actual tax liability and making informed property investment decisions.
What Is the Section 24 Tax Credit System?
Section 24, fully implemented since April 2020, restricts mortgage interest relief to the basic rate of income tax. This means landlords receive a 20% tax credit mortgage interest relief regardless of their marginal tax rate.
The calculation works in two stages:
- Calculate income tax on rental profits without deducting mortgage interest
- Apply a 20% tax credit based on allowable mortgage interest payments
This differs dramatically from the pre-2017 system where mortgage interest was fully deductible against rental income before tax calculations.
How the 20% Basic Rate Tax Credit Calculation Works
The section 24 basic rate credit follows a specific calculation method that often catches landlords off-guard. Here's the step-by-step process:
Step 1: Calculate Gross Rental Profit
Add up all rental income and deduct allowable expenses (excluding mortgage interest). Allowable expenses include:
- Letting agent fees
- Property management costs
- Repairs and maintenance
- Insurance premiums
- Safety certificates and compliance costs
- Legal and professional fees
Step 2: Add to Other Income
Include the gross rental profit with your other income (employment, self-employment, pensions, dividends) to determine your total taxable income and marginal tax rate.
Step 3: Calculate Income Tax
Apply income tax rates to your total income. From April 2027, property income will be taxed at separate rates (22% basic, 42% higher, 47% additional), but currently uses standard income tax rates.
Step 4: Apply the 20% Tax Credit
Calculate 20% of your allowable mortgage interest payments and deduct this from your income tax liability.
Worked Example: Section 24 Tax Credit in Practice
Consider Sarah, a higher-rate taxpayer with the following rental property situation:
- Rental income: £24,000
- Allowable expenses (excluding mortgage): £4,000
- Mortgage interest: £8,000
- Other income: £60,000
Under the Current System:
Rental profit (before mortgage interest): £24,000 - £4,000 = £20,000
Total taxable income: £60,000 + £20,000 = £80,000
Income tax on rental profit: £20,000 × 40% = £8,000
Section 24 tax credit: £8,000 × 20% = £1,600
Net tax on rental income: £8,000 - £1,600 = £6,400
Pre-2017 System (for comparison):
Rental profit (after mortgage interest): £24,000 - £4,000 - £8,000 = £12,000
Income tax on rental profit: £12,000 × 40% = £4,800
The difference? Sarah pays £1,600 more in tax annually due to Section 24 restrictions.
Key Limitations of the 20% Tax Credit
The section 24 tax credit 20% system has several important limitations that affect its practical value:
Tax Credit Cannot Exceed Tax Liability
The tax credit cannot reduce your income tax bill below zero. If your 20% mortgage interest tax credit exceeds your total income tax liability, you lose the excess relief.
No Relief Against Other Taxes
The tax credit only reduces income tax. It cannot be offset against National Insurance contributions, student loan repayments, or other taxes.
Impact on Marginal Tax Rates
Because rental profits are included in full before applying the tax credit, landlords may be pushed into higher tax brackets, affecting the taxation of their other income.
Which Mortgage Interest Qualifies for the Tax Credit?
The 20% tax credit mortgage interest relief applies to most forms of property-related borrowing:
- Buy-to-let mortgage interest
- Second charge loans for property purchase or improvement
- Bridging finance interest
- Development finance interest (subject to trading income rules)
However, certain restrictions apply:
- Interest must relate to residential property letting
- The property must be let on a commercial basis
- Interest on commercial property mortgages remains fully deductible
Section 24 and Different Tax Rates
The impact of the section 24 basic rate credit varies significantly depending on your marginal tax rate:
Basic Rate Taxpayers (20%)
Basic rate taxpayers typically see minimal impact from Section 24, as their effective relief remains at 20%. However, they may be pushed into higher tax brackets by including gross rental profits.
Higher Rate Taxpayers (40%)
Higher rate taxpayers face the most significant impact. Their effective mortgage interest relief drops from 40% to 20%, substantially increasing their tax bills.
Additional Rate Taxpayers (45%)
Additional rate taxpayers see their effective relief drop from 45% to 20%, creating the largest absolute tax increases.
Planning Strategies for Section 24
Several strategies can help mitigate the impact of restricted mortgage interest relief:
Limited Company Structure
Holding properties through a limited company allows full mortgage interest deduction against rental profits. However, incorporation involves additional complexity and costs.
Maximising Other Allowable Expenses
Focus on claiming all available property expenses that remain fully deductible. Our comprehensive guide to landlord tax deductions covers allowable expenses in detail.
Portfolio Optimisation
Consider the overall tax efficiency of your property portfolio, including disposal strategies and reinvestment decisions.
Record Keeping for Section 24 Tax Credits
Accurate record keeping becomes even more critical under Section 24. You need to maintain detailed records of:
- All mortgage interest payments throughout the tax year
- Loan statements showing interest portions of payments
- Documentation linking borrowing to specific rental properties
- Evidence of commercial letting arrangements
With Making Tax Digital requirements becoming mandatory from April 2026, digital record keeping will be essential.
Common Section 24 Tax Credit Mistakes
Landlords frequently make errors when calculating their section 24 tax credit 20% relief:
Including Capital Repayments
Only the interest portion of mortgage payments qualifies for the tax credit. Capital repayments provide no tax relief.
Applying Credit Against Wrong Taxes
The tax credit only reduces income tax liability. It cannot be offset against National Insurance or other taxes.
Overlooking the Tax Credit Cap
Some landlords assume they can claim unlimited tax credits, but the relief cannot exceed their total income tax liability.
Future Changes to Property Tax Relief
From April 2027, property income will be subject to separate tax rates (22% basic, 42% higher, 47% additional rate). This change may affect how the Section 24 tax credit system operates, though the 20% basic rate relief principle is expected to remain.
These changes make it increasingly important to understand your current tax position and plan for future developments in property taxation.
Getting Professional Help with Section 24
The complexity of Section 24 calculations often justifies professional assistance. Property accountants specialising in landlord taxation can help optimise your tax position and ensure accurate compliance.
Consider professional advice if you:
- Own multiple properties with complex financing arrangements
- Are considering incorporation to avoid Section 24
- Have rental income pushing you into higher tax brackets
- Need help with MTD compliance and digital record keeping
The section 24 tax credit 20% system represents a permanent change to property taxation that affects millions of UK landlords. Understanding exactly how this basic rate relief works helps you make informed decisions about your property investments and tax planning strategies.
For comprehensive guidance on all aspects of rental income taxation, including Section 24 implications, refer to our complete guide to Section 24 tax relief.