If you're a UK landlord with a buy-to-let mortgage, Section 24 of the Finance (No.2) Act 2015 is arguably the single most impactful piece of tax legislation to hit your bottom line in the last decade. Fully phased in since April 2020, its effects are now compounding — pushing higher-rate taxpayers into eye-watering effective tax rates and forcing thousands of landlords to reconsider whether holding residential property in their personal name still makes financial sense.

In this guide, we break down exactly how Section 24 works, who it hurts the most, what strategies landlords are deploying in response, and why this legislation is creating one of the most significant waves of motivated sellers in the UK property market right now.

What Is Section 24 and Why Was It Introduced?

Section 24 — often referred to as the "tenant tax" by landlord advocacy groups — was announced by then-Chancellor George Osborne in the July 2015 Budget. The stated aim was to "level the playing field" between landlords and owner-occupiers. Before Section 24, individual landlords could deduct the full cost of their mortgage interest payments from their rental income before calculating their tax liability. This meant a landlord paying £8,400 per year in mortgage interest on a property generating £12,000 in annual rent would only be taxed on the £3,600 net profit.

The government argued this gave landlords an unfair advantage over first-time buyers competing for the same properties. Section 24 changed the rules so that mortgage interest could no longer be deducted as a business expense. Instead, landlords receive a basic rate tax credit — worth 20% of their mortgage interest costs — regardless of the tax band they actually fall into.

The change was phased in over four tax years:

Since April 2020, the restriction has been fully in effect. No mortgage interest can be deducted from rental income. The only relief available is the 20% basic rate credit. For basic-rate taxpayers, the net effect is broadly neutral. For everyone else, it's a significant tax increase — and in some cases, a devastating one.

How Section 24 Changed the Maths: A Worked Example

Let's look at a concrete scenario that illustrates why Section 24 is so punishing for higher-rate taxpayers. Consider a landlord with the following profile:

• Monthly rental income: £1,000 (£12,000/year)
• Monthly mortgage interest: £700 (£8,400/year)
• Other allowable expenses: £600/year
• Personal tax band: 40% higher-rate taxpayer

The tax bill has increased from £1,200 to £2,880 — a 140% increase. But the real sting goes deeper. The landlord's actual cash profit after mortgage interest and expenses is just £3,000 per year. Under Section 24, they're paying £2,880 in tax on that £3,000 — an effective tax rate of 96%.

And it gets worse still. Because the full rental income is now counted as taxable income (before the credit is applied), Section 24 can push landlords into higher tax bands, trigger the loss of their personal allowance (which starts tapering at £100,000 of adjusted net income), and even affect eligibility for child benefit through the High Income Child Benefit Charge. Some landlords are being taxed on income they never actually receive — they are, in effect, paying tax on their lender's money.

Who Is Hit Hardest?

Section 24 does not affect all landlords equally. The pain concentrates on specific profiles:

Higher-rate and additional-rate taxpayers. If you're in the 40% or 45% tax band (including via employment income), the gap between the tax you owe and the 20% credit you receive is substantial. The higher your marginal rate, the bigger the penalty.

Highly leveraged portfolios. Landlords who expanded aggressively using high loan-to-value mortgages during the pre-2015 era are disproportionately affected. If mortgage interest consumes 60–80% of your rental income, Section 24 can create scenarios where your tax bill exceeds your actual profit.

Northern England and lower-yield areas. In regions like the North East, parts of Yorkshire, and the Midlands, where rental yields are tighter and property values lower, margins were already slim. Section 24 has turned marginal properties into loss-makers. A two-bed terrace in County Durham generating £475/month with a £320/month mortgage simply doesn't survive the new tax arithmetic for a higher-rate taxpayer.

Accidental landlords and small portfolio holders. Many landlords with one or two properties — often people who inherited a property or couldn't sell during a downturn — lack the scale to justify the costs of incorporation and find themselves trapped between an unsustainable tax position and the expense of restructuring.

Strategies Landlords Are Using to Mitigate Section 24

1. Incorporation — transferring to a limited company. Companies are not affected by Section 24. A limited company can still deduct mortgage interest as a legitimate business expense and pays corporation tax (currently 25% for profits over £250,000, but just 19% effective rate for smaller profits via the marginal relief mechanism). For landlords building or holding long-term, this is often the most cited solution. However, transferring existing properties from personal ownership to a company triggers Capital Gains Tax and Stamp Duty Land Tax — costs that can run into tens or even hundreds of thousands of pounds. Some landlords use a "Section 162 incorporation relief" route, but HMRC has been increasingly sceptical of these claims, and specialist tax advice is essential.

2. Portfolio restructuring. Selling properties with the highest leverage ratios — particularly those where rents barely cover the interest after tax — removes the drag from the portfolio without triggering excessive gains tax if prices are still close to purchase values.

The Motivated Seller Opportunity

Section 24 is creating one of the most sustained waves of motivated sellers the UK has seen in decades. Landlords who cannot incorporate, cannot absorb the tax hit, and cannot sell quickly enough are often willing to accept below-market offers to achieve speed and certainty. Days on market for landlord-exit listings have climbed significantly in northern cities where yields were thinnest after the change.

For property investors, this is a structural buying opportunity. The seller is motivated by tax pain, not by market timing. They want out. That means price, speed, and chain-free completion matter more than achieving the highest possible sale price.

This article is for informational purposes only and does not constitute tax or financial advice. Consult a qualified tax adviser before making decisions about your property portfolio.