Buy-to-let property has long been a favourite investment vehicle for UK savers — tangible, leveraged, and historically appreciating. But the tax treatment of rental income and property gains has become substantially harsher since 2017, while the ISA retains its full tax-free wrapper. For many investors, running the numbers after tax produces a different picture than before.
How Rental Income Is Taxed (2025/26)
Rental income is added to your other income and taxed at your marginal rate:
- Basic rate (20%) if total income is below £50,270
- Higher rate (40%) if income is £50,271–£125,140
- Additional rate (45%) above £125,140
Allowable deductions include letting agent fees, maintenance and repairs, landlord insurance, and certain other costs. But the most significant deduction — mortgage interest — is no longer fully deductible.
Section 24: The Mortgage Interest Restriction
Prior to April 2020, landlords could deduct mortgage interest from rental income before calculating taxable profit, reducing their tax bill directly. Under Section 24 (fully phased in from 2020/21), this deduction was replaced with a 20% tax credit.
This change primarily hits higher rate taxpayers. A basic rate taxpayer still effectively deducts interest at 20%, so the net impact is neutral. A higher rate taxpayer used to deduct at 40% and now only gets a 20% credit.
Worked example — Higher rate taxpayer, 2025/26
- Annual rent received: £18,000
- Mortgage interest paid: £9,000
- Other allowable costs: £2,000
- Net rental income: £18,000 - £2,000 = £16,000 (interest not deductible)
- Income tax at 40%: £16,000 × 40% = £6,400
- Less: 20% tax credit on mortgage interest: £9,000 × 20% = £1,800
- Tax payable: £4,600
- Pre-tax rental profit: £18,000 - £9,000 - £2,000 = £7,000
- Tax as % of actual profit: 65.7%
Before Section 24, the same landlord would have paid: (£18,000 - £9,000 - £2,000) × 40% = £2,800 — a £1,800 lower bill.
Capital Gains Tax on Residential Property
When you sell a buy-to-let property, the gain is subject to Capital Gains Tax:
- Basic rate taxpayer: 18% on residential property gains (from April 2024)
- Higher/additional rate taxpayer: 24% on residential property gains
The annual CGT exempt amount is only £3,000 (from 2024/25) — reduced from £12,300 in 2022/23. This means most gains are taxable.
Additionally, you may face a recapture of capital allowances and must report and pay CGT within 60 days of completion (not on your annual self-assessment).
Example:
- Bought for £200,000, sold for £350,000
- Gain: £150,000
- Less annual exempt amount: £3,000
- Taxable gain: £147,000
- CGT at 24% (higher rate): £35,280
- Plus: 3% SDLT surcharge paid on purchase was not deductible from CGT… (it is deductible as enhancement expenditure)
Stamp Duty Land Tax Surcharge
Buy-to-let investors face a 3% SDLT surcharge on all property purchased in England (5% from October 2024 for additional dwellings). This materially increases the upfront cost compared to primary residence purchases, reducing the effective yield.
On a £250,000 property purchased after October 2024:
- Standard SDLT: £2,500
- Additional surcharge (5%): £12,500
- Total SDLT: £15,000
This is an upfront dead cost that immediately reduces your return on investment.
ISA: The Clean Alternative
Inside a Stocks and Shares ISA:
- No income tax on dividends or interest
- No capital gains tax on growth
- No reporting obligations
- Fully liquid: withdraw at any time
- Annual allowance: £20,000
A global equity index fund inside an ISA has historically returned 7–10% annually (long-term average), tax-free.
Direct Return Comparison
Buy-to-let example (higher rate taxpayer)
| Metric | Value |
|---|---|
| Property value | £250,000 |
| Annual rent | £13,750 (5.5% gross yield) |
| Mortgage interest (75% LTV at 5%) | £9,375 |
| Other costs | £1,500 |
| Taxable rental income (no mortgage deduction) | £12,250 |
| Tax at 40% | £4,900 |
| Less 20% credit on mortgage interest | £1,875 |
| Tax paid | £3,025 |
| Net rental income after tax | £13,750 - £9,375 - £1,500 - £3,025 = -£150 |
| Effective net yield (cash-on-cash) | Negative |
This illustrates that at 5% mortgage rates, a leveraged buy-to-let for a higher rate taxpayer may generate negative cash flow even before maintenance surprises, voids, or letting agent costs.
ISA equivalent
| Metric | Value |
|---|---|
| Investment | £62,500 (equivalent equity/deposit) |
| Expected return at 7% | £4,375 |
| Tax on returns | £0 |
| Net annual return | £4,375 (7.0%) |
Buy-to-Let Advantages ISA Cannot Match
- Leverage: A £250,000 property bought with a £62,500 deposit means any capital appreciation applies to the full £250,000, not just your equity — amplifying returns (and losses)
- Tangible asset: Physical property appeals to investors who want something they can see
- Inflation hedge: Property prices and rents have historically correlated with inflation over the long term
- Rental income growth: Rents can be increased over time; ISA dividends fluctuate
ISA Advantages Buy-to-Let Cannot Match
- Liquidity: You can sell ISA holdings within days; selling a property takes months
- Tax simplicity: No self-assessment, no CGT reporting within 60 days, no Section 24 complications
- Lower entry cost: No stamp duty, no solicitor fees, no mortgage arrangement fees
- Diversification: A global index fund is inherently diversified; a single property is highly concentrated
The Landlord Stress Test
The buy-to-let calculation also faces ongoing risks the ISA does not:
- Void periods (months without rent)
- Major maintenance bills (roof, boiler, structural)
- Difficult tenants and legal costs
- Regulatory changes (EPC requirements, tenants’ rights legislation)
- Remortgaging risk when fixed rates expire
Who Might Still Prefer Buy-to-Let?
- Lower rate taxpayers with no or minimal mortgage, where Section 24 is less damaging
- Investors with significant cash equity who do not rely on leverage
- Those who already maximise ISA allowance and pension and need additional investment capacity
- Investors in areas with very high yields (above 8–10%) that absorb the tax friction
The Bottom Line
For most higher rate taxpayers with access to ISA allowance, a Stocks and Shares ISA provides better after-tax returns than leveraged buy-to-let at current mortgage rates and after accounting for Section 24. Buy-to-let remains relevant for cash-rich investors or those who want leveraged exposure to property. Use our rental income tax calculator to model your specific buy-to-let tax position before committing.