How buy-to-let mortgages differ from residential ones
A buy-to-let mortgage is underwritten on completely different criteria from a standard residential loan. Rather than focusing mainly on your salary, lenders assess the expected rental income, which typically must cover 125% to 145% of the monthly mortgage payment, stress-tested at a notional interest rate of around 5% to 5.5%, regardless of the actual product rate. This rental-coverage test exists to ensure the property can still service the debt if rates rise or if you face a void period.
Most buy-to-let mortgages are interest-only, which keeps monthly payments lower and preserves cash flow, but means the capital balance is never reduced during the mortgage term. You'll need a plan to repay it, usually by selling the property or remortgaging at the end of the term. Deposits are larger than for residential purchases: 25% is the typical minimum, and the most competitive rates usually require 40%. Arrangement fees are also higher, often running to 1% to 2% of the loan, and some products charge a percentage fee rather than a flat amount.
Lenders also take a view on the type of property and the rental market. Houses of Multiple Occupation (HMOs), properties above commercial premises, studio flats and ex-local authority homes can all attract stricter criteria or require specialist lenders. If you're a higher-rate taxpayer, some lenders will apply a tighter stress test because your effective tax rate on profits is higher.
Upfront costs of a buy-to-let purchase
Plan for all of these before completion day.
| Cost item | Typical range | Notes |
|---|---|---|
| Deposit | 20% to 25% of price (40% for best rates) | Higher than residential; some specialist lenders require 30%+ |
| Additional-property SDLT surcharge (England/NI) | 5% on whole purchase price | On a £250,000 property that is an extra £12,500 vs a main-home purchase |
| Mortgage arrangement fee | £1,000 to £3,000 or 1%-2% of loan | Can often be added to the loan but increases interest cost |
| Mortgage valuation fee | £150 to £1,500 | Depends on lender and property value; some lenders include this free |
| Legal fees and searches | £1,200 to £2,500 | Disbursements and search fees on top of solicitor's own charges |
| Building survey | £400 to £1,500 | Recommended; a HomeBuyer Report or Level 3 Building Survey |
| Broker fee | £0 to £500 | Many whole-of-market brokers are fee-free and paid by lender commission |
On a £250,000 buy-to-let in England the stamp duty surcharge alone adds roughly £12,500 compared with buying as a main home.
Running costs that eat into rental yield
Gross rental yield (annual rent divided by property value) is a useful first screen, but the costs that sit between gross rent and actual profit in your pocket are substantial. Letting agent fees for a tenant-find-only service typically run to one month's rent plus VAT, while a fully managed service costs 10% to 15% of monthly rent plus VAT. For many landlords, particularly those with jobs or living far from the property, full management is essential rather than optional.
Maintenance is routinely underestimated. As a rough rule of thumb, set aside 1% of the property value per year for repairs and replacements: a boiler replacement costs £2,000 to £4,000, re-wiring an older house can be £5,000 to £10,000, and a full roof repair may run to £5,000 or more. Without a reserve fund these costs can wipe out several years of net rental income in one go.
Void periods, the gaps between tenancies when no rent comes in, are inevitable. A realistic assumption for budgeting is one month of voids per year, though the actual figure depends heavily on location and property type. During voids you still pay the mortgage, insurance and any service charges, so cash flow can quickly turn negative.
Annual ongoing costs to budget for
These apply every year, whether the property is tenanted or not:
- Letting agent management fees: typically 10% to 15% of rent plus VAT for a fully managed service.
- Landlord buildings insurance: roughly £150 to £400 a year depending on property type and location.
- Gas safety certificate (CP12): required annually, around £60 to £120.
- Electrical Installation Condition Report (EICR): required every five years for rental properties, typically £150 to £300.
- Energy Performance Certificate (EPC): required before letting; currently properties must achieve at least EPC band E (band C reforms are under consultation).
- Portable Appliance Testing (PAT): recommended if you supply electrical appliances.
- Maintenance and repairs contingency: budget 1% of property value per year as a minimum.
- Letting agent administration fees, renewal fees and check-in/check-out costs.
- For flats: service charges and ground rent or any equivalent if leasehold.
- Accountancy fees if you complete a self-assessment tax return for rental income.
Tax on buy-to-let income: Section 24 explained
Rental profit is taxed as income at your marginal rate, which is 20% for basic-rate taxpayers, 40% for higher-rate taxpayers, and 45% for additional-rate taxpayers. Until 2020, landlords could deduct the full mortgage interest as a business expense before calculating profit. Section 24 of the Finance Act 2015 removed that deduction in stages and replaced it with a 20% tax credit on the finance costs instead.
The impact is significant for higher-rate taxpayers. Suppose you receive £15,000 in rent, pay £8,000 in mortgage interest and have £2,000 in other expenses. Previously, taxable profit was £5,000. Under Section 24, taxable profit is £13,000 (rent minus other expenses only). A higher-rate taxpayer now pays 40% on £13,000 (£5,200) and then deducts the 20% credit on £8,000 (£1,600), giving a tax bill of £3,600, far higher than the £2,000 they would have paid under the old rules.
Some landlords have responded by holding property through a limited company, where mortgage interest remains fully deductible as a business expense and profits are subject to corporation tax (currently 25% for profits above £250,000 and 19% for profits below £50,000). However, company mortgages typically carry higher interest rates, and extracting profits as salary or dividends creates further tax. The right structure depends heavily on individual circumstances, so professional accountancy advice is essential before making the decision.
Illustrative net return on a £250,000 buy-to-let
Based on 5.5% gross yield, 25% deposit, interest-only mortgage at 5%, fully managed.
| Item | Annual amount |
|---|---|
| Gross rent (5.5% yield) | £13,750 |
| Management fees at 12% + VAT | -£1,980 |
| Insurance, safety certificates, repairs reserve | -£1,200 |
| Mortgage interest (75% LTV, 5%) | -£9,375 |
| Accountancy and misc | -£400 |
| Net cash flow before tax | £795 |
| Income tax at 40% on £12,150 profit (Section 24) | -£3,260 (offset by 20% credit on interest = £1,875 credit) |
| Net after tax (higher-rate taxpayer estimate) | approx. -£590 |
This example shows how Section 24 can turn a paper-positive cash flow into a net loss for higher-rate taxpayers. Numbers are illustrative; individual figures will vary.
Model the full picture before you commit
Higher deposits, the stamp duty surcharge, Section 24 tax treatment, rising insurance premiums and tightening EPC requirements have all compressed buy-to-let returns since 2016. A gross yield above 6% to 7% is generally needed in most regions for a higher-rate taxpayer to achieve a meaningful net return. Always run a full cash-flow model using realistic rents, voids and costs before purchasing.
Capital gains tax when you sell
Buy-to-let is not your main home, so when you eventually sell, any profit is subject to capital gains tax (CGT). Residential property gains are taxed at 18% for basic-rate taxpayers and 24% for higher and additional-rate taxpayers, after deducting your annual CGT exempt amount (£3,000 for 2024/25) and allowable costs such as stamp duty paid on purchase, legal fees and the cost of capital improvements.
CGT on UK residential property must be reported and paid to HMRC within 60 days of completion using the CGT on UK Property online service. Missing this deadline brings automatic penalties and interest. Where the property has been your main home at some point during ownership, letting relief and Private Residence Relief may reduce the CGT bill, but the rules are complex and specialist tax advice is strongly recommended before a sale.