Buy-to-Let Mortgages in 2026: The Rate Is Not the Return

The Bank of England history shows Bank Rate at 3.75% following its 18 December 2025 decision (checked 26 September 2026). It does not publish the price of the BTL fix you personally qualify for. The chart traces actual policy decisions, not buy-to-let offers.

NatWest explicitly separates buy-to-let from residential borrowing; its rate tool asks for property price, deposit and purpose, but did not display a usable product quotation when checked. We therefore do not pass off a residential market average or an unverified teaser rate as a current BTL offer. Ask a broker for the full illustration: interest rate, product fee, valuation, early-repayment charge, reversion rate and whether the fee is paid upfront or added to the debt.

For scale, on an assumed £225,000 interest-only loan, each one percentage point of interest costs £2,250 a year (£187.50 monthly). An assumed £2,000 arrangement fee spread over a two-year fix adds an economic £1,000 a year before any interest on a financed fee. Compare total cash over the expected holding period, not just the first monthly payment. A low initial rate with a large fee is not automatically the cheaper mortgage.

A buy-to-let loan is secured against a let property; affordability commonly depends on prospective rent and the lender’s own coverage test, not just your salary. The exact deposit, interest-coverage ratio, stress rate, treatment of existing commitments and minimum landlord income vary by lender. Never assume a generic stress rate is your approval rate. Interest-only keeps the principal outstanding: a sale or refinance must ultimately repay it. NatWest offers both repayment and interest-only BTL options.

Consider an illustrative £300,000 purchase with 25% down (£75,000), £225,000 borrowed, rent of £1,500 per month and a hypothetical 5.5% interest-only rate. Contracted rent is £18,000 a year, a 6% gross yield. Interest is £12,375 a year. One month empty cuts receipts to £16,500; allow £2,500 for insurance, management and repairs (assumptions, not published averages). Pre-tax cash is then £1,625, before any arrangement fee, stamp duty, tax or capital repairs.

At an illustrative 7% renewal rate, interest rises to £15,750 and the same property loses £1,750 before tax. The void is not an abstract risk: one empty month plus a one-point rate rise consumes £3,750 of cash relative to a fully let 5.5% year. Budget a liquid repairs and void reserve rather than counting projected rent as guaranteed income. For repayment-versus-interest-only mechanics see our interest-only mortgage guide.

HMRC’s finance-cost calculation says an individual residential landlord cannot deduct mortgage interest from taxable property profit; instead a basic-rate tax reduction is available, subject to the lower of finance costs, property profits and adjusted total income above the personal allowance. The full restriction has applied since April 2020. It is not an unconditional refund. HMRC’s rental-income guidance explains how rental income and allowable expenses enter property profits.

Using the example above and assuming all the £2,500 operating costs qualify, no other property profits or losses, enough adjusted income for full relief, and an England/Wales/Northern Ireland taxpayer whose entire extra property profit falls in the 40% band: taxable property profit is £16,500 − £2,500 = £14,000. Income tax before relief is £5,600; 20% × £12,375 interest = £2,475 reduction. Net incremental tax = £3,125. Actual cash after interest, operating costs and income tax is minus £1,500 a year. The £1,625 pre-tax surplus did not pay the tax bill.

For an otherwise identical 20% marginal-rate taxpayer with enough adjusted income, tax is £2,800 − £2,475 = £325; cash is £1,300. Both figures exclude the assumed arrangement fee: allocating a £2,000 fee over two years reduces simple economic annual returns by another £1,000, though its actual tax treatment depends on the loan and circumstances. These are marginal illustrations, not complete Self Assessment calculations; crossing bands, personal-allowance taper and the relief cap change the result. The 2026/27 HMRC allowances table gives a £12,570 personal allowance and the England/Wales/Northern Ireland higher-rate threshold of £50,270. Scottish income-tax treatment differs; get tailored tax advice.

HMRC’s additional-property rates for England and Northern Ireland from April 2025 are 5% on the first £125,000, 7% on the next £125,000 and 10% on the next slice to £925,000. For this assumed £300,000 additional home, that is £6,250 + £8,750 + £5,000 = £20,000 SDLT. This is not a universal UK stamp-duty calculation: Scotland and Wales have separate transaction taxes; exceptions and non-resident surcharges can change the bill. Our SDLT guide explains the bands.

The investor has committed at least £95,000 in deposit and SDLT, before legal work, survey, any mortgage fee and cash reserves. Even the basic-rate case’s £1,300 annual after-tax cash represents only about 1.37% on that £95,000 — not 6%. The higher-rate case loses money on that cash-flow measure. Neither result includes house-price movement, loan repayment, sale costs or capital gains tax. If selling, HMRC’s 2026/27 CGT guidance sets a £3,000 annual exempt amount and 18%/24% gain rates depending on taxable income and the size of the gain; you cannot assume the entire gain gets the lower rate. Compare with other uses of capital rather than treating the gross yield as your investment return.

Get comparable written illustrations for the same borrowing, LTV, fix duration and repayment method. Add fees and charges, and note if financing the fee increases interest and the exit balance. Ask whether the lender accepts the property type and expected rent; an HMO or limited-company application can have different underwriting and tax consequences. Do not incorporate merely to dodge Section 24: extraction tax, financing, administration and transfer costs need separate modelling.

Then run three rows on paper: fully let, one-month void and a higher refinancing rate. In each row subtract interest, realistic upkeep, fees and the tax due under your ownership structure. If the stressed row needs your salary to cover the mortgage, the purchase is a leveraged bet on price growth, not a self-funding income asset. Compare fixed and tracker mortgages only after the BTL-specific fees and approval terms are clear.