Section 24 has fundamentally changed how mortgage interest affects property tax calculations. To understand the real impact, let's examine a detailed case study of a landlord with £100k annual rental income.

This analysis shows the actual numbers, tax calculations, and strategic decisions facing many UK property investors today.

The Portfolio Profile

Meet Sarah, a higher-rate taxpayer with a substantial BTL portfolio:

  • Annual rental income: £100,000
  • Annual mortgage interest: £45,000
  • Other property expenses: £15,000 (repairs, insurance, management)
  • Main job salary: £60,000
  • Total gross income: £160,000

Before Section 24, Sarah's property business generated healthy profits. Now, the mortgage interest restriction creates a very different tax position.

Section 24 Tax Calculation Breakdown

Step 1: Taxable Rental Income

Under Section 24, mortgage interest is no longer fully deductible from rental income:

  • Gross rental income: £100,000
  • Less: Non-interest expenses: £15,000
  • Less: Mortgage interest (limited to 20%): £9,000
  • Taxable rental profit: £85,000

Previously, Sarah could deduct the full £45,000 mortgage interest, giving a taxable profit of just £40,000.

Step 2: Income Tax Calculation

Sarah's total taxable income becomes £145,000 (£60,000 salary + £85,000 rental profit):

  • Basic rate band (£0-£37,700): £7,540 tax
  • Higher rate band (£37,700-£125,140): £34,976 tax
  • Additional rate band (£125,140-£145,000): £8,938 tax
  • Total income tax: £51,454

Step 3: Mortgage Interest Tax Relief

Sarah receives 20% tax relief on the remaining £36,000 mortgage interest:

  • Mortgage interest not deducted: £36,000 (£45,000 - £9,000)
  • Tax relief at 20%: £7,200
  • Net income tax liability: £44,254

The Financial Impact

Comparing Sarah's position before and after Section 24 reveals the true cost:

Before Section 24 (2016/17)

  • Taxable rental profit: £40,000
  • Total taxable income: £100,000
  • Income tax liability: £26,500
  • After-tax rental income: £73,500

After Section 24 (2025/26)

  • Taxable rental profit: £85,000
  • Total taxable income: £145,000
  • Net income tax liability: £44,254
  • After-tax rental income: £55,746

Annual tax increase: £17,754

This represents a 67% increase in Sarah's tax bill, purely due to Section 24. Her effective tax rate on rental profits has jumped from 26.5% to 44.3%.

Additional Considerations

Child Benefit Clawback

Sarah's increased taxable income triggers the high income child benefit charge. With two children receiving £2,212 annual child benefit, her income above £60,000 results in a full clawback of £2,212.

Personal Allowance Loss

Sarah loses £7,970 of her personal allowance (£145,000 - £125,140 = £19,860 ÷ 2). This creates an additional tax charge of £3,188 at 40%.

These hidden charges add another £5,400 to Sarah's annual tax bill.

Strategic Options Analysis

Option 1: Continue as Individual

Total annual tax impact: £23,154 (including child benefit and personal allowance effects)

This reduces Sarah's net rental income to approximately £22,000 annually - a 70% reduction from her pre-Section 24 position.

Option 2: Incorporation

Moving the properties into a company structure could provide relief. Our calculators suggest potential savings, but incorporation involves:

  • Stamp duty on property transfers (typically 3-5%)
  • Capital gains tax on deemed disposals
  • Ongoing corporation tax and dividend tax
  • Additional administrative burden

For Sarah's portfolio, incorporation might save £8,000-£12,000 annually after all costs.

Option 3: Portfolio Restructuring

Sarah could consider:

  • Reducing mortgage debt through property sales
  • Switching to interest-only mortgages with lower rates
  • Investing in properties with higher yields
  • Diversifying into commercial property (unaffected by Section 24)

The Incorporation Decision Process

Given the £23,154 annual tax impact, Sarah needs professional advice on incorporation timing and structure. Key factors include:

  • Current property values vs purchase prices
  • Available reliefs and elections
  • Long-term investment strategy
  • Administrative capacity

Many landlords in Sarah's position find that incorporation pays for itself within 2-3 years, despite the upfront costs.

Key Takeaways

This case study demonstrates that Section 24 can eliminate most or all profit from highly-mortgaged BTL portfolios. For landlords with £100k+ rental income, the tax impact often exceeds £20,000 annually.

The restriction doesn't just increase tax - it can push landlords into higher rate bands, trigger benefit clawbacks, and reduce personal allowances. These combined effects create effective tax rates above 50% on rental profits.

Professional tax planning becomes essential at this level. Whether through incorporation, portfolio restructuring, or timing strategies, there are usually ways to mitigate Section 24's impact.

However, each situation requires individual analysis. What works for Sarah might not suit another landlord with different circumstances, property types, or long-term goals.

If you're facing similar challenges with a substantial property portfolio, consider speaking to specialists who understand both the tax implications and practical solutions. Our services include detailed Section 24 impact assessments and incorporation feasibility studies.