Interest-Only vs Repayment Buy-to-Let: Which Is Better for UK Property Investors in 2026?

Around three-quarters of all outstanding buy-to-let mortgage balances in the UK are on interest-only terms, according to FCA data — and most landlords chose that structure without ever modelling the repayment alternative. On a £180,000 BTL mortgage at 4.8%, choosing interest-only over repayment adds roughly £430/month to your cash flow. Over 25 years, the repayment borrower owns the same asset debt-free while the interest-only landlord still owes £180,000. Neither outcome is automatically wrong — but choosing without running the numbers is.

The short answer: interest-only buy-to-let mortgages maximise monthly cash flow and purchasing power, making them the default for most active investors. Repayment mortgages build equity automatically, carry lower end-of-term risk, and can reduce your Section 24 exposure in a personal-name portfolio. The right structure depends on your exit plan, tax position, and whether you're building an income engine or a debt-free asset base.

How each product works

On an interest-only mortgage, every monthly payment covers only the cost of borrowing — the interest. If you borrow £180,000 at 4.8%, your monthly interest payment is £720. After 25 years of making that payment, you still owe £180,000 — the capital is intact. The lender will expect a credible repayment vehicle: for residential mortgages this is tightly regulated, but for buy-to-let the accepted strategy is typically property sale or remortgage.

On a repayment (capital and interest) mortgage, each monthly payment covers the interest due plus a portion of the original loan balance. Early in the term the split is mostly interest; by year 20 it is mostly capital. At the end of the 25-year term, the mortgage balance is zero and you own the property outright. The monthly payment on the same £180,000 at 4.8% is approximately £1,020 — roughly £300 more than interest-only for the same loan at the same rate. That £300 difference is the cost of automatic equity building.

Side-by-side comparison

Feature	Interest-Only BTL	Repayment BTL
Monthly payment (£180k @ 4.8%, 25yr)	£720	~£1,020
Cash flow advantage	+£300/month	Baseline
Loan balance after 25 years	£180,000	£0
Equity growth via mortgage payments	None	Full capital repaid
End-of-term refinancing risk	High	None
Maximum loan from same rental income (ICR)	Higher	Lower
Section 24 tax credit exposure (personal name)	Greater (higher interest cost)	Lower (smaller interest cost in later years)
Suitable for limited company (SPV)?	Yes — Section 24 avoided	Yes
Exit strategy required?	Yes — sale, remortgage or savings	No — property owned outright

The cash flow case for interest-only

Cash flow is why interest-only dominates the BTL market. The monthly saving is material and compounds across a portfolio.

Take a standard northern England two-bed terraced house: purchase price £140,000, 75% LTV BTL mortgage at 4.8%, so a loan of £105,000. Monthly rent: £750. Here is how the two structures compare:

• Interest-only: Monthly payment = £420. Net cash flow before tax = £750 − £420 = £330/month.
• Repayment: Monthly payment = ~£595. Net cash flow before tax = £750 − £595 = £155/month.

The interest-only investor pockets £175 more per month — £2,100 per year — on this single property. Across a five-property portfolio, that differential is worth over £10,000 annually in additional cash flow that can be reinvested into further deposits, maintenance reserves, or living income. This compounding effect is why experienced investors almost universally default to interest-only while they are in active acquisition mode.

"Interest-only buy-to-let mortgages account for the majority of outstanding BTL balances by value in the UK — the cash flow advantage during the holding period is the primary driver of that preference among professional property investors." — Financial Conduct Authority, Mortgage Market Study data

The equity case for repayment

Repayment borrowers build equity from two sources simultaneously: capital growth in the property's market value, and the gradual reduction of the mortgage balance. Interest-only landlords benefit only from the first. On a 25-year hold, this distinction is substantial.

Using the same northern terraced example — £140,000 purchase, £105,000 loan — here is what each investor holds after 25 years, assuming the property grows at 3.0% per annum (broadly in line with the long-run average shown in the Nationwide House Price Index):

• Property value after 25 years at 3.0% p.a.: approximately £293,000
• Interest-only investor's equity: £293,000 − £105,000 outstanding = £188,000
• Repayment investor's equity: £293,000 − £0 outstanding = £293,000

The repayment investor holds £105,000 more equity at the end of the term — equivalent to the original loan balance. They achieved this by paying an extra £175/month, totalling £52,500 in additional mortgage payments over 25 years, and ending up with £105,000 more equity net. The difference is the interest saved on the reducing balance over the full term, which makes repayment genuinely more efficient on a long hold — provided the investor does not need the cash flow during the holding period.

"UK residential property has delivered average annual capital growth of approximately 3–4% over the past two decades, with significant regional variation." — Nationwide House Price Index, historical series

Tax implications: how Section 24 changes the calculation

Section 24 — the restriction on mortgage interest relief for landlords who hold buy-to-let property in their personal name — is one of the most significant factors in the interest-only vs repayment decision for 2026.

Under Section 24, landlords cannot deduct mortgage interest from rental income to calculate their taxable profit. Instead, they receive a 20% tax credit on interest paid. For basic-rate taxpayers, this is broadly neutral. For higher-rate (40%) or additional-rate (45%) taxpayers, it creates a tax bill on money they have not actually earned — what critics call "phantom income."

The mechanism that matters here: on an interest-only mortgage, the interest payment is at its maximum for the entire term. On a repayment mortgage, the interest element of each monthly payment declines each year as the outstanding balance falls. By year 20 of a 25-year repayment mortgage, the monthly interest payment may be under half of what it was in year one.

For a higher-rate taxpayer in a personal-name portfolio:

• Interest-only: Higher and fixed interest cost → larger Section 24 tax liability for the full 25-year term
• Repayment: Declining interest cost → Section 24 tax liability reduces progressively over the term as the loan balance falls

The cleanest solution to Section 24 is buying through a limited company (SPV), which can still deduct mortgage interest as a business cost. For investors already holding property personally, the repayment vs interest-only tax difference is worth modelling carefully with an accountant before the next remortgage.

How lenders use ICR stress tests — and why it favours interest-only

Most BTL lenders apply an Interest Coverage Ratio (ICR) test to determine the maximum loan they will advance. The standard formula: monthly rental income must equal at least 125–145% of the monthly mortgage payment (stressed at a rate of typically 5.5–7.5%), depending on the lender and whether the property is held personally or in a company.

Because interest-only monthly payments are lower than repayment payments on the same loan, the same rental income supports a larger interest-only loan. This is not a small difference:

• Example: Monthly rent £1,000. ICR ratio 125% (basic rate landlord). Stressed rate 5.5%.
• Maximum interest-only loan: £1,000 ÷ 1.25 = £800/month allowable interest payment → loan of £174,500 at 5.5%
• Maximum repayment loan: The same £800/month stressed payment on a capital-and-interest basis over 25 years at 5.5% supports a loan of approximately £133,000

Interest-only gives the investor access to roughly £41,500 more capital on this property at the same rental income. For investors who are LTV-constrained rather than income-constrained, this can be decisive in whether a deal is fundable at all. This structural advantage is one reason why professional landlords overwhelmingly use interest-only during the portfolio-building phase.

When each structure is the right choice

Interest-only suits you when:

• You are in active portfolio growth mode and need to maximise cash flow to fund further deposits
• The property is in a limited company (SPV), eliminating Section 24 exposure on the higher interest cost
• You have a clear, funded exit — planned sale or a credible remortgage plan before term-end
• You are LTV-constrained and need the greater purchasing power that interest-only ICR calculations provide

Repayment makes more sense when:

• You are a higher-rate taxpayer holding property personally and the Section 24 impact of a full interest-only term is material
• You want the property owned outright at term-end with no refinancing risk or dependence on property values
• You are approaching the end of your mortgage-able career and need certainty of ownership
• Your cash flow is strong enough that the additional repayment cost does not compromise returns

Modelling your own numbers

Many experienced UK property investors use interest-only on properties they intend to refinance or sell within 10 years, and repayment on long-term hold assets held personally where the Section 24 calculation becomes more favourable over time. A practical rule of thumb: if the property is in a limited company and you are in portfolio growth mode, interest-only is almost always correct. If the property is held personally, you are a higher-rate taxpayer, and you intend to hold for 20+ years, run the numbers on repayment first.

Use the rental yield calculator to model gross and net returns under both structures, and the deal analyser to stress-test ICR at the lender's stressed rate. The choice between interest-only and repayment is one of the highest-leverage structural decisions in a BTL portfolio — worth the twenty minutes it takes to model.

Frequently asked questions

Is interest-only or repayment better for buy-to-let in the UK?

Most UK landlords choose interest-only for the £200–£450/month cash flow advantage. Repayment builds equity automatically and eliminates refinancing risk at term-end. The right choice depends on your exit strategy and tax position — many experienced investors use interest-only during portfolio growth and switch to repayment for long-term hold assets held personally.

Do lenders treat interest-only and repayment BTL mortgages differently?

Yes. ICR stress tests mean the same rental income supports a higher loan on interest-only (lower monthly payment) than on repayment. This gives interest-only borrowers greater purchasing power at a given rental level — a key reason it dominates the BTL market.

How does Section 24 affect the choice between interest-only and repayment BTL?

Section 24 restricts personal-name landlords from deducting mortgage interest costs from rental income for tax purposes — they receive a 20% tax credit instead. On an interest-only mortgage, the interest payment is fixed and high for the full term, meaning the Section 24 liability is at its maximum throughout. On repayment, the interest element declines each year, so the Section 24 exposure reduces progressively. For higher-rate taxpayers holding property personally, this is a meaningful argument for repayment — or for restructuring into a limited company where mortgage interest is still fully deductible.

What happens at the end of an interest-only BTL mortgage term?

At term-end, the full original capital balance falls due. On a £180,000 interest-only BTL, after 25 years the borrower still owes £180,000. The three exit routes are: sell the property and use the proceeds to clear the loan; remortgage onto a new deal if LTV and age allow; or repay from other savings or assets. The risk is that property values may not have grown sufficiently, or that the borrower's age or income restricts their ability to remortgage. This repayment risk is the key argument against interest-only for investors without a clear, funded exit plan.