An interest-only mortgage means your monthly payments cover only the interest charged on the loan — none of it reduces the amount you actually borrowed. At the end of the mortgage term, the full original loan amount is still owed and must be repaid in one go. This is very different from a standard repayment mortgage, where each payment gradually clears both interest and capital until the balance reaches zero.
Why the monthly payments look so much lower
Because you're only paying interest, monthly costs on an interest-only mortgage are noticeably lower than an equivalent repayment mortgage — sometimes by several hundred pounds a month on a typical loan. This is the main appeal, particularly for landlords managing buy-to-let cash flow, or for older borrowers wanting to reduce outgoings. But the lower payment is not free money — it simply defers the repayment of the capital to a single lump sum at the end.
The repayment vehicle requirement
Because the full loan is due at the end of the term, residential lenders will almost always require evidence of a credible "repayment vehicle" — a separate plan to build up enough money to clear the capital by the end of the mortgage. Common repayment vehicles include:
- A stocks and shares ISA or other investment plan being paid into regularly
- Pension tax-free cash, where the amount and timing are clearly evidenced
- Another property or investment expected to be sold
- Regular savings into a dedicated account
Lenders will usually want to see evidence that the vehicle is realistically on track to cover the balance, not just a vague intention, and may review this periodically during the mortgage term.
Why lenders are far stricter than they used to be
In the years before the 2008 financial crisis, interest-only mortgages were often sold with little to no scrutiny of the repayment plan — some borrowers had no vehicle at all, simply hoping house prices would rise enough to sell and clear the debt. Regulatory changes since then have tightened this considerably. Lenders now require documented evidence of a repayment strategy at the point of application, and many mainstream lenders restrict interest-only lending to borrowers with a high enough deposit (often 50% loan-to-value or lower for residential, though buy-to-let terms differ) and a minimum income level.
Repayment vs interest-only: a simple comparison
| Repayment mortgage | Interest-only mortgage | |
|---|---|---|
| Monthly payment | Higher | Lower |
| Balance at end of term | Zero (if payments kept up) | Full original loan still owed |
| Total interest paid over term | Lower | Higher, since capital never reduces |
| Requires a separate plan | No | Yes — a credible repayment vehicle |
Common mistakes
- Treating the lower monthly payment as "affordable" without a genuine plan for the lump sum at the end
- Assuming house price growth alone will cover the shortfall — this is exactly the assumption that left many borrowers unable to repay after 2008
- Not reviewing the repayment vehicle's progress periodically to check it's still on track
What to do next
If you're on an interest-only mortgage, contact your lender well before the term ends to discuss your repayment plan — leaving it too late significantly narrows your options. If you're considering interest-only for a new mortgage, be realistic about whether your chosen repayment vehicle will actually cover the balance, and get independent financial advice before committing.