An interest-only mortgage can look appealing on paper, with monthly payments considerably lower than an equivalent repayment mortgage. But that lower payment comes with a fundamental catch that every borrower needs to understand clearly before choosing this route.
How interest-only mortgages work
With an interest-only mortgage, your monthly payments cover only the interest charged on the loan — none of it reduces the actual amount you borrowed. At the end of the mortgage term, the full original capital sum is still owed in one lump sum, meaning you need a credible, verifiable plan to repay it.
Interest-only vs repayment: the core trade-off
| Interest-only | Repayment | |
|---|---|---|
| Monthly payment | Lower | Higher |
| Balance at end of term | Unchanged (full original loan) | Zero, assuming payments are kept up |
| Total interest paid | Higher over the full term | Lower over the full term |
| Requires a repayment strategy | Yes — mandatory | No |
Acceptable repayment strategies lenders require
Since regulatory reforms following the financial crisis, mainstream residential lenders require evidence of a credible repayment strategy before approving an interest-only mortgage. Commonly accepted strategies include a stocks and shares ISA or other investment vehicle building toward the target sum, endowment policies, pension lump sums, or a clear, evidenced plan to downsize or sell another property. Simply stating an intention to "sell the house" is often not accepted as a standalone strategy for a main residence, since it assumes property values will rise and doesn't provide somewhere to live afterward.
Why residential interest-only has become harder to access
Following widespread concern about borrowers reaching the end of interest-only terms without a viable repayment plan, mainstream lenders tightened criteria significantly, and interest-only on a main residence is now a smaller, more carefully underwritten part of the market than it once was — though it remains genuinely available for borrowers who can evidence a sound repayment strategy.
Where interest-only remains common
- Buy-to-let mortgages: Widely available on an interest-only basis, since landlords typically plan to sell or remortgage the property, or use rental profits, to repay the capital.
- Retirement Interest-Only (RIO) mortgages: A specific later-life product where the loan is typically repaid from the eventual sale of the property.
- Part-and-part mortgages: A hybrid where part of the loan is on interest-only terms and part on repayment, offering a middle ground between the two.
Risks worth taking seriously
Questions to ask yourself before choosing interest-only
- Is my repayment strategy realistic, evidenced, and something a lender is likely to accept?
- Am I comfortable that its value could underperform, and do I have a fallback plan?
- Would I be better served by a part-and-part mortgage, balancing lower payments with some capital reduction?
- Have I reviewed how this fits with my wider retirement and long-term housing plans?
For related reading, see our guides on Mortgages for Older Borrowers: Options Explained and Buy-to-Let Mortgage Rules Explained for UK Landlords.
To run your own numbers, try our Mortgage Repayment Calculator.
The bottom line
Interest-only mortgages genuinely lower your monthly outgoings, but they shift the responsibility for repaying the capital entirely onto you and your chosen strategy. They can be a sensible tool — particularly for buy-to-let or later-life lending — but for a residential main mortgage, they demand a realistic, well-evidenced repayment plan reviewed regularly, ideally alongside a mortgage adviser.