An interest only mortgage sounds simple: lower monthly payments, more flexibility, more cash available each month. And in the right circumstances, it can genuinely be a smart financial tool. But there’s a catch that catches a lot of borrowers off guard: the loan doesn’t shrink. Not by a penny. At the end of the term, you owe every pound you originally borrowed all in one go.
This guide explains exactly how interest only mortgages work, who they suit, what lenders require, the genuine risks involved, and how they compare to a standard repayment mortgage. The goal is to give you enough information to make a properly informed decision or at least know the right questions to ask your adviser.
Please note: this article is for general information only and doesn’t constitute financial advice. Always speak with a qualified mortgage adviser before making any borrowing decisions.
What Exactly Is an Interest Only Mortgage?
With a standard repayment mortgage, your monthly payment covers two things: the interest on the loan, and a portion of the capital (the amount you originally borrowed). Over the term typically 25 years you gradually pay off both. By the end, you own the property outright.
With an interest only mortgage, your monthly payment covers only the interest. The capital stays exactly where it was on day one. So, if you borrow £200,000, your payments keep the loan ticking along without reducing that balance at all. At the end of the term, you owe £200,000 in one lump sum.
This is why interest only is sometimes called deferred borrowing. You’re not avoiding the debt — you’re postponing it. For a broader overview of how mortgage interest works, the FCA’s mortgage guide is a useful starting point.
Is an Interest Only Mortgage Worth It?
The honest answer: it depends on your situation. The monthly savings are real and meaningful. But so is the end-of-term obligation. Here’s a straightforward way to think about it:
Interest only makes sense when you have a credible, reviewed repayment strategy already in place; you’re a buy-to-let investor whose rental income covers the monthly payments while the property appreciates; or you’re expecting a significant capital sum before the term ends from a property sale, pension, or inheritance.
A repayment mortgage is usually the better choice if you don’t have a clear plan for repaying the capital, you’re buying a primary residence and long-term security matters more than lower monthly costs, or you simply want the peace of mind of knowing you’ll own the property outright at the end.
What Does an Interest Only Mortgage Cost Month to Month?
Monthly payments are noticeably lower than a repayment mortgage for the same loan amount and rate. As an illustration: on a £200,000 mortgage at 3% over 25 years, an interest only mortgage would cost around £500 per month. The equivalent repayment mortgage would cost roughly £950 per month.
That £450 monthly difference is genuinely significant particularly for landlords and higher-income borrowers managing cash flow. But keep in mind: over 25 years, you’d pay around £150,000 in interest on the interest only product and still owe the original £200,000. With a repayment mortgage, you’d pay more each month but own the property outright at the end.
The Repayment Vehicle: This Is the Critical Part
Every lender offering an interest only mortgage will ask the same question: how do you intend to repay the capital at the end of the term? Your answer needs to be credible, specific, and realistic. This is called your repayment vehicle.
Common repayment vehicles include ISA savings and investment portfolios, pension lump sums, endowment policies (less common now than they used to be), proceeds from the sale of the property, or expected inheritance or other capital. Lenders typically review your repayment plan at intervals during the term if your circumstances change significantly, you’ll need to demonstrate an alternative.
The key risk: investment-based repayment vehicles don’t come with guarantees. If your ISA underperforms or your pension falls short, you could reach the end of the term unable to repay the full balance. That’s not just inconvenient it’s a serious financial position.
Who Qualifies for an Interest Only Mortgage in the UK?
Residential interest only mortgages have strict eligibility criteria. Most mainstream lenders require a high personal income Barclays, for instance, requires a minimum of £75,000 for a single applicant or £100,000 combined for joint applications. Some lenders set thresholds at £100,000 per applicant.
Loan-to-value limits are tighter too. Many lenders cap interest only lending at 50% of the property’s value, meaning you need a substantial deposit or a strong equity position. First-time buyers are unlikely to qualify through mainstream lenders.
Buy-to-let interest only mortgages are considerably more accessible. Most landlords opt for interest only because rental income can typically cover the interest payments, while the property itself serves as the intended long-term repayment vehicle. If your credit history is a concern, our article on whether you can get a mortgage with bad credit is worth reading before you apply.
What Happens If You Can’t Repay at the End of the Term?
This is the question that doesn’t get asked enough and it’s important to have an honest answer before you take out an interest only product.
When your term ends, your lender will contact you in advance usually one to two years beforehand to confirm your repayment plan. If the plan has fallen short, your options include extending the mortgage term (subject to reassessment), switching to a repayment basis for the remaining years, remortgaging to a new lender, or selling the property and using the proceeds to clear the balance.
If none of those routes is available, the lender can ultimately repossess. This does happen. It’s not hypothetical. A regularly reviewed, realistic repayment strategy is not an optional extra it’s the foundation the whole arrangement rests on.
Can You Switch from Interest Only to Repayment?
Yes, in most cases. If at some point you decide you’d rather start paying down the capital, you can usually switch to a repayment basis. Your monthly payments will increase sometimes significantly, particularly if there’s less term remaining than the original. But you’ll begin reducing your debt and will own the property outright at the end.
Note that switching back from repayment to interest only is generally not permitted. So, think carefully before making the change once you’ve moved to repayment, you’re typically committed.
If you’re thinking of switching lenders at the same time, our guide on how long it takes to remortgage gives a clear picture of the timeline involved.
Part-and-Part Mortgages: A Middle Option Worth Knowing About
There’s a third option between full repayment and full interest only: a part-and-part mortgage. This splits your borrowing part on a repayment basis, part on interest only. You reduce the capital somewhat each month, but keep payments lower than a pure repayment product. The lump sum you’ll owe at the end is smaller than with a full interest only deal. It suits borrowers who want to manage cash flow but also want to make some progress on the capital.
Frequently Asked Questions
What Is the Minimum Income for An Interest Only Mortgage in the UK?
Most residential lenders require a minimum income of £75,000 to £100,000 per applicant. Some lenders set combined income thresholds for joint applications. Buy-to-let interest only products typically use different criteria based on rental yield rather than personal income.
Can A First-Time Buyer Get an Interest Only Mortgage?
It’s very unlikely through mainstream lenders. Residential interest only products are designed for higher-income borrowers with significant deposits. First-time buyers are generally better served by repayment mortgages.
What Happens at The End of An Interest Only Mortgage?
You must repay the full capital the original amount borrowed in a single lump sum. If your repayment vehicle hasn’t kept pace, you’ll need to extend the term, remortgage, or sell the property to clear the balance.
Is Interest Only Good for Buy-To-Let?
It’s a common strategy in buy-to-let because rental income can cover the monthly interest while the property (hopefully) appreciates in value. That said, it still requires a credible exit plan and regular review particularly in a changing property market.
Can You Overpay on An Interest Only Mortgage?
Yes. Most lenders allow overpayments often up to 10% of the balance per year on fixed rate deals, with more flexibility on variable rate products. Overpaying reduces the capital you’ll owe at the end, which can be a sensible strategy if your finances allow it.
Is An Interest Only Mortgage Risky?
It carries more inherent risk than a repayment mortgage, because the capital obligation never reduces over time. That risk is manageable with proper planning and a realistic, reviewed repayment strategy but for borrowers who take it out without a solid plan, serious difficulty at the end of the term is a real possibility.