Section 24 of the Finance (No. 2) Act 2015 was fully phased in by April 2020, but most UK landlords still underestimate its real bite. The problem isn't just that mortgage interest is no longer deductible — it's that your taxable rental profit is now much higher than your cash profit, which pushes people into the higher-rate band, tapers the Personal Allowance above £100,000, and can even trigger the High Income Child Benefit Charge.
This is called phantom income. In 2026, with BTL mortgage rates still around 5%, phantom income is at its most painful since Section 24 was introduced.
This guide explains exactly how Section 24 inflates your taxable income, walks through three worked scenarios and then covers four legal strategies to mitigate the bill — ordered from least disruptive to most.
How Section 24 actually works
Pre-2017, landlords deducted mortgage interest from rent like any other expense. From April 2020 that relief was replaced by a flat 20% basic-rate tax credit on mortgage interest.
Taxable profit formula now:
Taxable profit = Rent − Allowable expenses (excluding mortgage interest)
Then at the tax calculation stage:
Tax = Taxable profit × marginal rate − (Mortgage interest × 20%)
For a basic-rate landlord this works out the same. For anyone above the basic-rate threshold (£50,270 total income in 2026), it always costs more tax than the old rules.
Worked example: the phantom income trap
Landlord Sarah earns £40,000 PAYE from a day job and owns one BTL:
Under old rules (pre-2017)
Taxable rental profit = £18,000 − £9,500 − £3,000 = £5,500
Total income: £40,000 + £5,500 = £45,500 → basic rate
Tax on rental profit: £5,500 × 20% = £1,100
Under Section 24 (2020–onwards)
Taxable rental profit = £18,000 − £3,000 = £15,000
Total income: £40,000 + £15,000 = £55,000 → £4,730 now in higher-rate band
Tax on rental profit: (£10,270 × 20%) + (£4,730 × 40%) = £2,054 + £1,892 = £3,946
Less 20% credit on mortgage interest: £9,500 × 20% = £1,900
Tax due: £2,046
Cash profit is the same both ways (£5,500). Tax bill nearly doubled — and Sarah's effective marginal rate on her job income has gone up too.
Phantom income side effects (the bit most guides miss)
Because Section 24 inflates your taxable income, it can also trigger:
One landlord we spoke to lost her full Personal Allowance and claim to child benefit in the same year — despite barely breaking even on cash.
Four legal ways to mitigate Section 24 in 2026
1. Transfer to your lower-earning spouse (Form 17)
If your spouse is in a lower tax band (or has no income), you can shift beneficial ownership via Form 17 and a declaration of trust. Best for jointly owned properties where you file as tenants-in-common.
2. Switch to a limited company (SPV)
Inside a ltd co, mortgage interest is fully deductible before corporation tax (19–25% in 2026). Section 24 does not apply.
Trade-offs (covered in our SPV transfer guide):
Break-even for a higher-rate landlord is typically 3–4+ properties.
3. Pension contributions (extend the basic-rate band)
Every £1 of pension contribution effectively extends your basic-rate band by £1. A higher-rate landlord paying £10,000 into a SIPP pushes £10,000 of rental profit back into the 20% band, saving £2,000 in tax on top of the £2,000 pension tax relief.
4. Overpay the BTL mortgage
Every £1,000 of mortgage reduction cuts interest by ~£50/year. For a higher-rate landlord Section 24 makes that £50 saving worth ~£35 after tax — effective return ~3.5% tax-free and compound. Often beats equity funds for pure cash-flow landlords.
FAQs
Does Section 24 apply to furnished holiday lets (FHLs)?
Since April 2025, FHLs lost their special tax treatment — Section 24 now applies to FHLs as well.
Does Section 24 apply in Scotland?
Yes. Section 24 is UK-wide. Scottish Income Tax bands differ (starter 19%, intermediate 21%, higher 42% etc.) but the interest-relief restriction is identical.
Can I incorporate my portfolio without triggering CGT?
Only via Incorporation Relief (s162 TCGA), which requires you to run the portfolio as a genuine business (usually 20+ hrs/week, multiple properties, active management). Get specialist advice — HMRC rejects weak claims.
Does Section 24 apply to limited companies?
No. Ltd co BTL deducts interest normally before corporation tax.
Where to go next
Start your 14-day LetCompliance trial to log every deductible expense per property — critical for MTD ITSA quarterly reporting from April 2026.
Frequently asked questions
What is Section 24 phantom income?
"Phantom income" is the difference between your cash profit (rent minus all expenses including mortgage) and your taxable profit (rent minus expenses but excluding mortgage interest). Because Section 24 doesn’t let you deduct mortgage interest, your taxable profit can be tens of thousands of pounds higher than your cash profit — income you never actually receive but still get taxed on.
Does Section 24 apply to limited-company landlords?
No. Section 24 only affects landlords owning BTLs in their personal name. A limited company (SPV) deducts mortgage interest fully before corporation tax. This is why many higher-rate landlords consider incorporation — see our [SPV transfer guide](/blog/spv-limited-company-buy-to-let-2026-transfer-costs).
Can pension contributions reduce Section 24 tax?
Yes. Every £1 of pension contribution extends your basic-rate band by £1, so you save 20% tax on each pound of rental profit pushed back into the basic-rate band — on top of standard pension tax relief. Works particularly well where phantom income has pushed you just into the higher-rate band.
Does Section 24 apply to furnished holiday lets (FHLs)?
Yes, as of April 2025. The FHL tax regime was abolished in Finance Act 2024, and FHLs are now taxed the same as long-term lets — Section 24 applies in full.