How an interest-only mortgage actually works
On a standard repayment mortgage, each monthly payment covers two things: the interest charged on the loan, and a portion of the loan itself. Over time the balance reduces and eventually reaches zero at the end of the term.
On an interest-only mortgage, your monthly payment covers only the interest. The original loan stays exactly the same throughout. At the end of the term — which might be 20 or 25 years away — the full original amount is still outstanding and needs to be repaid in one go.
The appeal is straightforward: lower monthly payments. The trade-off is that you need a credible plan for how you’re going to repay the capital at the end.
Mortgage amount: £300,000 at 4.5% — 25-year term
Repayment mortgage: Approximately £1,667/month
Interest-only mortgage: Approximately £1,125/month
That’s a difference of around £542 per month — but at the end of the term, the full £300,000 still needs to be repaid on the interest-only version.
Who interest-only suits — and who it doesn’t
Interest-only is not inherently riskier than a repayment mortgage — it depends entirely on whether the repayment strategy is sound. For the right borrower with the right plan, it can be a sensible and tax-efficient way to structure a mortgage. For someone without a credible repayment route, it creates a problem that compounds over time.
Borrowers who tend to be well-suited to interest-only include:
- Those with significant investment portfolios who prefer to keep capital working rather than paying down the mortgage
- Higher earners who want to manage monthly cash flow and have clear assets available at the end of the term
- Landlords — interest-only is standard on buy-to-let, where the property itself is the repayment vehicle
- Older borrowers with substantial equity who plan to downsize
- Those approaching retirement with pension lump sums that will cover the remaining balance
It’s less suitable for those whose only plan is “the property will have gone up in value” without having thought through what that means in practice — particularly if they couldn’t actually afford to repay the loan from a sale without significant financial difficulty.
What lenders require today
Interest-only criteria tightened significantly after the financial crisis, when large numbers of endowment-backed mortgages matured with shortfalls. Today’s lenders are considerably more cautious about who they’ll lend to on this basis.
Most lenders require:
- A minimum income — many set this at £75,000 or £100,000 for single applicants, though this varies
- A minimum equity or deposit — many lenders require at least 25% equity, some 50% for the most flexible products
- A credible repayment strategy — this needs to be evidenced, not just stated. Vague references to “investments” or “future income” are unlikely to be accepted
- A maximum loan size — some lenders cap the amount they’ll lend on interest-only terms
Not all lenders publish their interest-only criteria openly. Some products are only available through brokers, and criteria can change. Knowing which lenders are currently active in this space and what they require is part of what we do.
Repayment strategies — what lenders actually accept
The repayment strategy is the central question on any interest-only application. Lenders don’t just ask what your plan is — they assess whether it’s realistic and whether there’s evidence it will work.
Sale of the property
The most commonly cited strategy — and one most lenders will accept, provided the numbers make sense. If you’re planning to sell and downsize at the end of the term, lenders don’t just check that the sale proceeds will cover the outstanding mortgage. They often require a minimum level of equity to remain in the property at the end of the term — typically expressed as a percentage of the property’s value.
The reasoning is practical: if downsizing is your repayment strategy, the lender wants confidence that after repaying the mortgage you’ll have enough left to actually buy something smaller in the same area. Some lenders express this as a percentage — a minimum equity requirement of 25–50% is common. Others set a fixed minimum cash amount, for example £250,000 or £300,000, calibrated to reflect what a smaller property in the local area is likely to cost. The idea is that if property prices haven’t moved dramatically, or circumstances change before you reach the end of the term, there’s still a realistic and viable path available to you.
Investment portfolio or ISA
A stocks and shares ISA, investment portfolio, or similar asset can be acceptable, but lenders typically want to see the current value and will apply a discount to account for market risk. They’re unlikely to accept projected future values at face value — they want to see what you have now and whether it’s on track.
Pension lump sum
For those approaching retirement, the tax-free lump sum from a pension can be a legitimate repayment vehicle. Lenders will want to see pension statements showing projected values and may apply criteria around how close to retirement you are.
Sale of another property
If you own another property — a buy-to-let or a second home — the proceeds from its eventual sale can be used. Lenders will assess the equity in that property and how realistic the sale is.
Combination strategies
In many cases, the repayment plan is a combination of the above — some downsizing proceeds, some investment, some pension. Lenders are generally comfortable with this provided the combined picture is credible.
The repayment strategy conversation is one where being upfront and specific matters. Vague answers create problems. The more clearly you can articulate your plan and evidence it, the smoother the application process.
Part-and-part mortgages
A part-and-part mortgage is exactly what it sounds like — part repayment, part interest-only. You borrow the total amount but split it into two portions. One portion is on a capital repayment basis, gradually reducing over time. The other portion is interest-only, with a repayment strategy attached.
This is a useful middle ground for borrowers who want lower monthly payments than a full repayment mortgage but also want to reduce their overall borrowing over time — rather than having the full original loan outstanding at the end of the term.
Not all lenders offer part-and-part, and those that do have different criteria for the split. It’s worth exploring as an option if a full interest-only mortgage feels like too much of a stretch but a full repayment mortgage stretches the budget too far.
Interest-only in later life — RIO mortgages
For older borrowers, there is a specific product category called a Retirement Interest Only mortgage (RIO). Unlike a standard interest-only mortgage, a RIO has no fixed end date — the loan runs until you die, move into long-term care, or sell the property. Monthly payments cover the interest only, keeping the loan balance stable.
RIOs are assessed on retirement income — pension, investment income, or similar — rather than employment income. They sit between a standard interest-only mortgage and a lifetime mortgage in terms of how they work.
See our blog post on RIO mortgages as an alternative to equity release for a detailed comparison.
Can you switch from repayment to interest-only?
Yes, in many cases. Most lenders will consider a switch for existing customers, subject to meeting their current criteria. It’s worth knowing that the criteria applied may be stricter than for a new application — lenders are aware that this is often motivated by financial pressure rather than strategic planning, and will want to be satisfied that the repayment strategy is sound.
If you’re considering switching because your circumstances have changed and the repayment mortgage has become unaffordable, it’s important to have an honest conversation about what the alternatives are and what the long-term implications would be.
We’ll assess your situation and repayment strategy honestly before making any recommendation. Call 01277 564 054.
Our fees for interest-only mortgage advice
No charge for initial conversations. For purchases, the broker fee is £195, payable on full application. For remortgages, including switches to interest-only, there is no broker fee. See our full fee schedule.
Frequently asked questions
On an interest-only mortgage, your monthly payment covers only the interest on the loan — not the loan itself. The original amount borrowed remains the same throughout the term and needs to be repaid at the end, usually through a sale of the property, an investment, a pension, or another agreed strategy.
Interest-only criteria has tightened considerably since the financial crisis. Lenders typically require a higher income, a larger deposit or equity stake, and a credible, evidenced repayment strategy. Eligibility varies significantly between lenders.
Commonly accepted strategies include the sale of the property (downsizing or moving), an investment portfolio or ISA, a pension lump sum, the sale of another property, or a combination of these. Lenders vary in what they accept and how they assess the credibility of each strategy.
A part-and-part mortgage splits your borrowing between interest-only and capital repayment. You pay interest on the full amount but also make capital repayments on a portion, gradually reducing part of the loan. This is a useful middle ground for those who want lower payments but also want to reduce their borrowing over time.
Possibly. Most lenders will consider a switch to interest-only for existing customers, subject to meeting their current criteria for income, loan-to-value, and repayment strategy. The criteria applied can be stricter than for a new application.
Some lenders offer interest-only products specifically for older borrowers, assessed on pension and other retirement income. This is sometimes called a retirement interest-only mortgage (RIO) and is separate from lifetime mortgages.
No charge for initial conversations. For purchases, the broker fee is £195, payable on full application. For remortgages, there is no broker fee.