Many landlords wonder whether Section 24 interest only mortgage restrictions affect their tax position differently compared to repayment mortgages. The answer might surprise you: Section 24 treats all mortgage interest the same way regardless of your mortgage type, but the overall financial impact varies significantly.
This guide examines how Section 24 interacts with different mortgage structures and what it means for your tax planning as a BTL investor.
Section 24 Basics: Same Rules for All Mortgage Types
Section 24 restricts mortgage interest relief to a 20% tax credit rather than a full deduction against rental income. This applies equally whether you have:
- Interest-only BTL mortgages
- Repayment mortgages
- Offset mortgages
- Commercial mortgages (though these are exempt from Section 24)
The key point: Section 24 doesn't distinguish between mortgage types. It simply caps your interest relief at the basic rate of tax regardless of your marginal rate.
For example, if you pay £8,000 annual mortgage interest, you'll get a £1,600 tax credit (20% of £8,000) whether that interest comes from an interest-only or repayment mortgage.
Interest Only BTL Tax Implications Under Section 24
Interest-only mortgages typically involve higher interest payments since you're not reducing the principal balance. This creates specific tax challenges under Section 24:
Higher Interest Payments Mean Bigger Section 24 Impact
Consider a £300,000 BTL property with an 80% mortgage (£240,000):
- Interest-only at 5%: £12,000 annual interest
- Repayment at 5%: approximately £8,500 interest in year one
Under Section 24, a higher rate taxpayer loses more tax relief with the interest-only option:
- Interest-only: loses £2,400 in tax relief (20% of £12,000)
- Repayment: loses £1,700 in tax relief (20% of £8,500)
Cash Flow Considerations
Interest-only mortgages often provide better monthly cash flow despite the Section 24 penalty. Using the same example with £1,500 monthly rent:
- Interest-only: £1,500 rent - £1,000 interest = £500 gross monthly surplus
- Repayment: £1,500 rent - £1,400 payment = £100 gross monthly surplus
However, the higher interest creates a larger tax bill, reducing the net benefit significantly.
Repayment vs Interest Only Landlord Tax Comparison
Let's examine a detailed comparison for a higher rate taxpayer with a £200,000 mortgage on a property generating £18,000 annual rent:
Interest-Only Scenario (5% rate)
- Annual interest: £10,000
- Rental profit (before interest): £18,000 - £2,000 other costs = £16,000
- Taxable profit: £16,000 (interest no longer deductible)
- Income tax: £6,400 (40% on £16,000)
- Less interest tax credit: £2,000 (20% of £10,000)
- Net tax: £4,400
Repayment Scenario (5% rate, year 1)
- Interest portion: £7,500
- Principal portion: £3,000
- Taxable profit: £16,000 (only interest matters for tax)
- Income tax: £6,400
- Less interest tax credit: £1,500 (20% of £7,500)
- Net tax: £4,900
The interest-only option actually produces a lower tax bill in this example, though the difference narrows over time as repayment mortgage interest decreases.
Long-Term Tax Planning Strategies
The choice between interest only BTL tax strategies and repayment options affects your long-term tax position:
Capital Growth vs Income Strategy
Interest-only mortgages are often preferred when:
- You expect significant capital growth
- You plan to refinance or sell within 10-15 years
- You want to preserve capital for additional investments
Repayment mortgages suit investors who:
- Want to build equity automatically
- Prefer reducing debt exposure over time
- Plan to hold properties long-term
Portfolio Expansion Considerations
Interest-only mortgages free up cash flow for portfolio growth, but Section 24 makes this strategy more expensive. Many landlords now consider incorporating their portfolio to avoid Section 24 entirely.
Alternative Strategies to Mitigate Section 24
Both mortgage types face Section 24 restrictions, but several strategies can help:
Limited Company Structure
Companies are exempt from Section 24, making both interest-only and repayment mortgages more tax-efficient. Corporation tax at 19-25% often beats the effective rates individual landlords face.
Offset Mortgages
Some landlords use offset mortgages to maintain flexibility. You can switch between effectively interest-only (maximum offset) and repayment (reduced offset) based on your tax position each year.
Commercial Property Investment
Commercial properties remain exempt from Section 24. Interest-only commercial mortgages provide full tax deductibility of interest payments.
When Interest-Only Still Makes Sense
Despite Section 24, interest-only BTL mortgages can still be optimal when:
- Cash flow priority: You need maximum monthly cash flow for living expenses or reinvestment
- Capital appreciation focus: Properties are in high-growth areas where capital gains outweigh the tax penalty
- Short-term holding: You plan to sell or refinance before the interest-only period expires
- Other income sources: You have business profits or pension income that keeps you in basic rate tax
Making Tax Digital and Record Keeping
With Making Tax Digital mandatory from April 2026, accurate record keeping becomes crucial regardless of mortgage type. You'll need to track:
- Monthly interest payments
- Principal payments (for capital gains calculations)
- All allowable expenses
- Quarterly income and expenditure
Interest-only mortgages are slightly simpler to track since all payments are potentially allowable expenses (subject to Section 24 restrictions).
Tax Planning Beyond 2027
From April 2027, property income faces separate tax rates (22% basic, 42% higher, 47% additional). This change affects the Section 24 calculation:
- Current system: 20% tax credit on interest
- Post-2027: 22% tax credit on interest (basic rate)
This slight improvement helps both mortgage types, but higher rate property taxpayers will face even larger tax bills, making incorporation more attractive.
Professional Advice and Planning
The interaction between Section 24 and different mortgage structures requires careful analysis of your specific circumstances. Consider speaking with a specialist property accountant who can:
- Model the tax impact of different mortgage options
- Assess whether incorporation makes sense for your portfolio
- Help with MTD compliance preparation
- Plan for the 2027 tax changes
The choice between interest-only and repayment mortgages involves more than just Section 24 – it affects your overall investment strategy, cash flow, and long-term wealth building approach.