Interest-Only vs Repayment: Which Is Better for Buy-to-Let?
July 25, 2026
Interest-only or repayment: which mortgage actually makes a buy-to-let investor more money? My answer is that the mortgage label doesn’t decide it. What matters is what you do with the money, what you want the property to achieve and how much risk you’re comfortable carrying.
I understand why landlords like interest-only mortgages. The monthly payment is lower, leaving more cash available for repairs, reserves and the next investment. I also understand why somebody outside property thinks the arrangement sounds strange. After twenty-five years of payments, you can still owe the original loan.
In my video published on 25 July 2026, I compared the two using the same property and mortgage rate. Once you follow the money beyond the monthly payment, the choice becomes much clearer. Interest-only is usually the stronger growth tool in my view; repayment is usually the stronger safety tool. Neither works well without a plan.
You can also watch my interest-only versus repayment comparison on YouTube.
The £200,000 property example
Imagine buying a £200,000 rental property with a 25% deposit. You put in £50,000 and borrow £150,000 over twenty-five years. To make the comparison fair, I used a constant mortgage rate of 5% for both options.
The interest-only payment is £625 a month. A standard repayment calculation gives approximately £877 a month, so the difference is about £252. These are illustrations, rather than current mortgage offers, and exclude fees and the other costs of buying and running the property.
If rent and operating costs are identical, interest-only leaves that extra £252 in your bank account each month. That can be very useful. But it isn’t £252 of extra profit created out of thin air: the repayment borrower is using the higher payment to reduce the amount owed.
This is the distinction I want investors to understand. Cash flow describes money moving in and out. Equity describes the value you own after debt. You can improve one while leaving the other unchanged, so looking only at the monthly payment gives an incomplete answer.
Where you stand after ten years
With those assumptions, the repayment mortgage falls to approximately £110,887 after ten years. Around £39,113 of the original debt has been cleared. The interest-only mortgage still stands at £150,000.
If the interest-only borrower spent the monthly saving, the repayment borrower now has about £39,000 more equity in the same property. Both have benefited equally from any change in the property’s value; the difference here comes from the debt.
What if the interest-only borrower kept the saving in cash earning nothing? Ten years of contributions would produce approximately £30,226. That is useful accessible money, but it is still below the debt reduction achieved through repayment.
The gap exists because reducing the mortgage balance also reduces future interest. More of the fixed repayment can then go towards clearing capital. It is a gradual process, which is why I wouldn’t judge a repayment mortgage only by how slowly the balance moves in the first few months.
Investing the difference changes the comparison
Now suppose the interest-only borrower invests the monthly difference instead. At the same 5% rate, compounded monthly, that investment would reach approximately £39,113 after ten years. In this simplified calculation, it matches the debt cleared by the repayment borrower.
One person has reduced a liability; the other has built an asset alongside an unchanged liability. That mathematical relationship is useful, but it doesn’t make the two arrangements equally risky or equally suitable.
Using a constant illustrative return of 7%, the investment pot would be about £43,597 after ten years. At 9%, it would be approximately £48,743. That puts the investment route roughly £4,484 or £9,630 ahead of the mortgage debt reduction, respectively.
For consistency, these figures use the unrounded monthly saving of approximately £251.89, contributions at the end of each month and the stated annual rate divided by twelve. They exclude investment charges and tax, assume every contribution is made and do not model the uneven returns of real markets.
The practical comparison is between the effective cost of borrowing and the return you actually keep after costs and tax. Mortgage tax treatment can also differ according to ownership structure. A headline investment return higher than the mortgage rate doesn’t automatically mean you come out ahead.
A saving and a hoped-for return are different things
Paying down debt at a fixed 5% rate avoids interest on that repaid capital while that rate applies. You don’t need an investment market to rise for that saving to happen. The benefit can change when the mortgage rate changes, and overpayment limits or charges matter if you make additional repayments.
A 7% or 9% investment return is an assumption, not a promise. Markets can fall, sometimes just when you need access to the money. A good long-term average doesn’t tell you what the investment will be worth on the day your mortgage must be repaid.
This is why I keep returning to risk and behaviour. An attractive spreadsheet can assume that you contribute every month, leave the investment alone and never panic. Real people face unexpected bills, changing priorities and uncomfortable market falls.
If you know that spare cash usually becomes extra spending, repayment may be a better fit than a theoretically superior investment strategy you won’t follow. There’s nothing unsophisticated about choosing a structure that helps you stick to your own intentions.
What happens over the full twenty-five years?
At the end of the repayment mortgage’s scheduled term, the debt is cleared, provided the agreed payments have been made. With interest-only, the original £150,000 remains due unless you have repaid capital separately.
Under the same constant 9% investment illustration, investing the monthly difference for twenty-five years produces approximately £282,394. On paper, that would cover the £150,000 loan and leave money over. At 5%, the model produces exactly the amount needed to match the debt repayment.
That is the case for interest-only: preserve cash flow, put it to productive use and potentially build more wealth than you would by clearing debt alone. But the mortgage liability is contractual; the investment outcome is uncertain.
You need a credible way to repay the capital. Selling, using investments or refinancing all have conditions and risks. The FCA’s work on interest-only mortgage repayment plans highlights why leaving that question until maturity can cause problems. Its consumer mortgage guidance should not be confused with the regulatory treatment of every business buy-to-let loan.
Why portfolio builders value the flexibility
My example involved one property, but the cash-flow difference becomes larger across several properties. Five otherwise identical mortgages would leave roughly £1,260 a month outside the properties on an interest-only basis.
Over five years, that is around £75,600 before investment returns, tax differences or additional costs. In the video I also illustrated how investing that amount at 7% could take it to roughly £90,000. Again, that is a modelled outcome rather than a forecast.
Cash outside the property can pay for a refurbishment, cover a void or contribute towards another deposit. Equity inside a repayment mortgage isn’t automatically available for those jobs. Accessing it usually means selling or arranging further borrowing, with fresh costs and lender checks.
That is why interest-only can help somebody build a portfolio sooner. However, using the saving to acquire more property also creates more exposure to borrowing, tenants, maintenance and market conditions. Scaling only helps if the additional purchases are sound and the whole portfolio remains manageable.
Repayment gives you a larger equity cushion
Consider a price fall after those first ten years. If the £200,000 property falls by 20%, it is worth £160,000. Against the repayment balance of about £110,887, there is approximately £49,113 of equity before selling costs. Against the interest-only balance of £150,000, there is just £10,000.
The repayment loan has a lower loan-to-value ratio and more room to absorb a falling valuation. That can make a difference when you refinance, although it never guarantees approval. Lenders also consider rental coverage, the borrower, the property and their own criteria.
This comparison looks at equity in the property itself. If the interest-only investor has built a separate investment pot, that asset also belongs in the overall assessment. We shouldn’t ignore it merely because it sits in a different account.
Equally, we shouldn’t assume it will retain its value during a property downturn. Several assets can fall together. I would want to know both how much wealth exists on paper and how much reliable cash is available when something needs paying.
Match the mortgage to the job
Someone with one or two properties who wants to become debt-free may prefer repayment. Someone building a portfolio may prefer interest-only because the cash can be recycled. Age, income, reserves, future plans and willingness to take risk all affect the decision.
There is also a middle ground. You might retain flexibility during refurbishments and reduce debt later, or use different mortgage structures across different properties. Any overpayments need to fit the lender’s rules, and changing the arrangement requires checking affordability and terms.
My guide to buy-to-let mortgage rates and cash flow looks at the wider borrowing-cost question. If you’re considering an investment account alongside property, my index funds guide explains the approach without assuming smooth or guaranteed returns.
For me, interest-only makes sense when the cash has a better, clearly defined job to do. Repayment makes sense when reducing debt best serves the plan. The important bit is deciding that before you choose the mortgage, then actually following through.
If you want to discuss how property fits your wider goals, book a free property strategy call. You can also explore Starter Club or explore Done For You and a 20-minute suitability call. For a personal mortgage recommendation, speak to an appropriately qualified mortgage adviser.