Interest-only mortgages: the gap at the end
The short answer
The balance never falls. Borrow £200,000 on interest-only and you owe £200,000 at the end, no matter how many years of payments you have made without missing one.
The lower payment is a deferral, not a saving. You pay interest on the full amount for the whole term, so the total cost is higher than on a repayment mortgage.
The plan for repaying the capital is the whole product. Everything else is detail. If the plan is vague, the mortgage is a problem waiting for a date.
If the end is approaching and you have no plan, act now. Options exist and they narrow sharply as time runs out. Contacting the lender early is the single most useful thing you can do.
What you are actually agreeing to
On a repayment mortgage, each monthly payment covers the interest for that month and chips away at the amount borrowed. Do that for twenty-five years and the debt reaches zero on its own.
On interest-only, the payment covers the interest and nothing else. The capital sits untouched for the entire term. This is not a defect or a trap; it is the product working exactly as intended. The lender is lending you money and charging you for it, and at the end you give the money back in one piece.
The consequence is easy to state and easy to underestimate. A borrower who has paid perfectly for twenty-four years and eleven months owes precisely what they borrowed. There is no partial credit for good behaviour.
See the difference Interest-only mortgage calculatorThe monthly cost on interest-only, the equivalent repayment figure, and the capital still owed at the end of the term. Formula and assumptions shown, and nothing you enter is stored or transmitted.
Cheaper monthly, more expensive overall
Both things are true at once, which is why the product is so frequently misunderstood.
The monthly payment is lower, often substantially, because none of it is repaying debt. That is real and it is the reason people choose it.
The total interest is higher, because interest is charged on the amount outstanding, and on interest-only that amount is the full sum for every month of the term. A repayment mortgage charges interest on a balance that shrinks year after year, so the same rate produces far less interest overall.
Comparing the two on monthly payment alone is comparing a smaller obligation now against a larger one later, and it is worth doing the comparison properly before deciding which suits you.
The repayment strategy is the product
Lenders require a credible plan for producing the capital before they will grant an interest-only mortgage, and they may revisit it during the term to check it is still on course. The plan is not paperwork. It is the thing that determines whether this ends well.
The common approaches fall into a few groups, and their reliability varies considerably.
| Strategy | What to think about |
|---|---|
| Savings or investments built alongside | Requires actually making the contributions, every year, for decades. Investment returns are uncertain, so a plan that only works if growth meets a target is a plan with a shortfall risk built in. Check the projection against the balance regularly rather than at the end. |
| Selling the property | Straightforward if you were always going to sell, and genuinely risky otherwise. It assumes the property is worth enough at a date you do not choose, and it means moving out. Ask where you would live afterwards, and whether the answer is affordable. |
| Downsizing | A version of the above with a plan for the next home. Works best where the current property is genuinely larger than you will need and the local price gap is wide enough to leave something over. |
| Selling another asset | Another property, a business, an investment portfolio. Reasonable where the asset is real and liquid enough, less so where it is one thing whose value could move against you. |
| An expected lump sum | Bonuses, inheritance, a pension lump sum. Lenders vary in how much weight they give these, and some will not accept them at all. Anything that depends on another person's decisions or lifespan is the weakest kind of plan. |
Lender criteria on all of this differ widely, and change, so treat the table as a guide to the thinking rather than a statement of what any particular lender will accept. Your lender or a broker can tell you what applies to you.
Where it genuinely makes sense
Interest-only has a poor reputation earned mostly by how it was sold in the past, but it is a reasonable choice in specific situations.
It suits people with lumpy income, where a lower committed monthly payment is manageable and large irregular sums can be paid off the capital as they arrive. It suits landlords, where the property is an investment expected to be sold or refinanced and the arithmetic is run on rental yield rather than household budget. It suits people bridging a defined period, such as a few years of low income before a known change. And it can suit borrowers with substantial assets elsewhere who are making a deliberate choice about where their money works hardest.
What these have in common is that the capital repayment is genuinely planned rather than assumed. Where interest-only goes wrong is when it is chosen because a repayment mortgage was unaffordable, since that means the borrower could not afford the house and the shortfall was postponed rather than avoided.
Part and part
Less discussed than it deserves. A part-and-part mortgage puts some of the borrowing on repayment and some on interest-only, so the balance falls but not to zero.
It suits someone whose repayment strategy will cover a portion of the debt with reasonable confidence but not the whole of it. Rather than gambling on the strategy stretching further than it can, you shrink the amount it needs to cover. The monthly payment sits between the two extremes.
It is also a useful destination for someone on full interest-only who wants to reduce the risk but cannot afford a wholesale switch to repayment. Worth asking your lender about specifically, because it is not always offered unprompted.
If the end of the term is coming
This is the section that matters most, and the message is simple: the earlier you engage, the more options exist.
Lenders write to interest-only borrowers as the term approaches. Those letters are worth opening even when the news is unwelcome, because a lender contacted with years remaining has considerably more room to help than one contacted after the balance has fallen due. Nobody at the lender wants to repossess a house; it is expensive, slow and a bad outcome for them too.
The options that may be available, depending on your circumstances, age, income and the property, include:
- Extending the term, which keeps the payment low and buys time, though it means paying interest for longer and lenders will consider your age and income.
- Switching to repayment, wholly or partly. The payment rises, sometimes steeply, but the debt then clears itself. Doing this earlier is far cheaper than doing it late, because there are more years to spread the capital over.
- Moving to part and part, as a middle route where full repayment is not affordable.
- A retirement interest-only mortgage, where interest continues to be paid monthly and the capital is repaid when the property is eventually sold, usually on death or a move into long-term care. These have their own criteria and are not right for everyone.
- Later-life lending or equity release, which can settle the balance but has significant long-term consequences for what is left of the property's value. This is regulated advice territory and should not be entered into without it.
- Selling, on your own timetable rather than under pressure, which almost always produces a better price and more choice than a forced sale.
Reducing the gap while you still can
If you have an interest-only mortgage and time remaining, there are things worth doing that do not require switching product.
Overpay where the terms allow it. Most mortgages permit a percentage of the balance to be overpaid each year without charge, and on interest-only every pound of overpayment reduces the capital permanently and reduces the interest charged from then on. Check your own limit before making a large payment.
Direct irregular money at the capital. A bonus or a windfall put against an interest-only balance does more work than it would against a repayment mortgage, because it reduces the sum you must find at the end as well as reducing interest.
Convert early rather than late. Switching some or all of the balance to repayment ten years before the end is far more affordable than five years before, since the capital spreads over twice as many payments. The instinct is to wait until the problem is urgent, which is exactly when it becomes hardest to solve.
What overpaying does Overpayment calculatorWhat paying extra saves in interest and how much sooner the balance clears, including one-off lump sums as well as regular amounts.
Buying with interest-only now
If you are considering taking one out rather than dealing with an existing one, the questions worth answering honestly are short.
What exactly will repay the capital, and what happens if that thing does not work out? Would a repayment mortgage on this property be affordable, and if not, is the property the right one? Have you compared the total cost rather than just the monthly payment? And are you comfortable that a plan you make today will still make sense in twenty years, when your circumstances will be different in ways you cannot currently predict?
If the answers are solid, interest-only is a legitimate tool. If the honest answer to the first question is that the house will probably be worth more later, that is a hope rather than a strategy, and it is worth saying so out loud before signing anything.