An interest only mortgage charges monthly payments that cover interest alone: the balance never falls and the full loan is repaid in one sum at term end, commonly after a 25 year term, from a repayment strategy agreed with the lender. Monthly costs run far below repayment mortgages, but total lifetime interest is higher and the strategy failing is the core risk.
TL;DR · LAST REVIEWED 25 JULY 2026
- Payments cover interest only; the original loan remains payable in full at term end
- Lenders must verify a credible repayment strategy at application and typically review it during the term
- Accepted vehicles: sale of the property with sufficient equity, investments and ISAs, endowments, pension tax free cash
- Retirement interest only (RIO) mortgages repay from the home's eventual sale on death or care entry, with affordability tested on the interest alone
- Part and part structures split a loan between repayment and interest only where full interest only fails criteria
KEY FACTS
- Monthly payment = interest on the full balance; capital element: zero
- Total interest over a full term exceeds a repayment mortgage on the same loan, because the balance never amortises
- Buy to let lending predominantly uses interest only: rent covers interest, sale or refinance handles capital
- Residential interest only typically requires stronger equity and income than repayment lending
- RIO mortgages: interest paid for life, capital repaid from the home's sale on death or long term care entry
- Regulators have repeatedly pushed lenders to engage early with borrowers approaching term end without full vehicles
The arithmetic, honestly
On a repayment mortgage each payment includes capital, so the debt amortises to zero. Interest only removes the capital element: every payment is lower, and the entire original loan remains at the end, with interest charged on the undiminished balance throughout.
The product is therefore a cash flow tool rather than a saving: it trades lower payments now for a repayment obligation later plus higher lifetime interest. Voluntary overpayments, where the product permits them, chip the capital and soften both.
Repayment strategies lenders accept
Regulated lenders must verify a plausible repayment vehicle at application. Commonly accepted: sale of the mortgaged property itself with minimum equity requirements, stocks and shares ISAs and other investments, endowment policies, pension tax free cash, and sale of other property.
Speculative plans are declined, and expected inheritances are accepted only rarely and cautiously. The vehicle underdelivering is the structural risk: shortfalls at term end force refinancing, term extensions where offered, or sale of the home.
Who the market serves
Buy to let sits naturally on interest only, which is why most landlord lending uses the structure. Residential interest only survives for borrowers with strong equity, higher incomes and clear vehicles, and two hybrid products widen access.
Retirement interest only mortgages serve older borrowers: interest is paid monthly for life and the capital repays from the eventual sale of the home on death or a move into care, with affordability tested on the interest payment alone.
Part and part mortgages split the loan between repayment and interest only, a middle path lenders increasingly offer when full interest only fails criteria.
Approaching term end
Borrowers on interest only approaching term end without a complete vehicle have options that improve with time remaining: switching to repayment, converting part of the loan, extending the term, refinancing to RIO, or selling.
Engaging with the lender early widens every option; waiting until expiry narrows them, which is why regulator guidance pushes lenders toward early contact with such borrowers rather than enforcement at the deadline.
RELATED GUIDES
DISCLAIMER
This article is editorial information, not financial advice. Kael Tripton Ltd is not authorised or regulated by the Financial Conduct Authority. Figures were correct at the last review date shown above; verify current rates and rules with the primary sources listed below before acting.
Frequently asked questions
What is an interest only mortgage?
A mortgage whose monthly payments cover only the interest, leaving the full original loan to repay in one sum at term end from a repayment strategy agreed with the lender at the outset.
Why are payments so much lower?
No capital is included: the payment is purely interest on the balance. The balance never falls, total interest over the term is higher, and the loan remains payable in full.
What repayment strategies do lenders accept?
Sale of the property with sufficient equity, investment portfolios and ISAs, endowments, pension tax free cash, or sale of other assets. Lenders verify plausibility at application and typically review during the term.
What is a retirement interest only mortgage?
A RIO product for older borrowers: interest is paid monthly for life and the capital repays from the home's eventual sale on death or a move into long term care.
Can I switch between interest only and repayment?
Usually, subject to affordability checks in the interest only direction. Part and part structures split a loan between the two, and voluntary overpayments reduce capital where permitted.
What happens if my repayment plan falls short?
Switching to repayment, extending the term, part conversion, refinancing to RIO, or sale. Early engagement with the lender widens every option.
SOURCES
- FCA: Mortgages – accessed 25 July 2026
- GOV.UK: Owning and renting property – accessed 25 July 2026
