Most countries have quietly standardized on repayment mortgages, where every payment chips away at both interest and principal. The UK is one of the few markets where interest-only is still a genuine, live choice for some borrowers — not just a legacy product from decades past — provided you can satisfy the lender's repayment vehicle requirements.
The Two Structures, Side by Side
Repayment mortgage: each monthly payment covers interest plus a portion of principal, following the same amortization curve used elsewhere — heavily interest-weighted early on, shifting toward principal over time. By the end of the term, the balance is fully cleared.
Interest-only mortgage: each monthly payment covers interest alone. The original loan balance never reduces through the payment itself — at the end of the term, the full amount is still owed, and needs to be repaid through some separate means: savings, investments, or sale of the property.
Worked Example
On the £262,500 loan from our Mortgage Calculator example, at 4.48% over 25 years:
| Structure | Monthly Payment | Balance at Year 25 |
|---|---|---|
| Repayment | ≈ £1,456 | £0 |
| Interest-only | ≈ £980 | £262,500 (unchanged) |
The interest-only payment is noticeably lower month to month — but the entire original balance is still due at the end, which is exactly why lenders now require documented proof of a credible repayment strategy before approving it.
Common Mistakes
Borrowers sometimes choose interest-only purely for the lower monthly payment without a concrete repayment plan, which is precisely the pattern lenders now screen against — an application without a credible, evidenced repayment vehicle is likely to be declined outright, not just questioned.
Borrowers also confuse "interest-only" with "buy-to-let default" — while interest-only is more common on BTL mortgages (where rental income services the interest and the property itself is often the exit strategy), it's not exclusive to buy-to-let, and residential interest-only still exists for qualifying borrowers.
A third mistake: underestimating how much total interest an interest-only mortgage costs over a long holding period, since the balance never shrinks — every year's interest is calculated on the full original amount, unlike a repayment mortgage where the interest charge shrinks as the balance does.
Where This Calculator Has Limits
It shows the two structures at their simplest — many borrowers actually use part-and-part mortgages, splitting a portion on repayment and a portion on interest-only, which this comparison doesn't model directly. It also can't verify whether a specific repayment vehicle would satisfy a given lender's requirements — that's a case-by-case underwriting decision.
Frequently Asked Questions
Can I still get an interest-only mortgage in the UK?
Yes, for qualifying borrowers who can evidence a credible repayment strategy — it's more restricted than it was pre-financial crisis, but it hasn't disappeared.
Is interest-only cheaper overall?
Monthly payments are lower, but total interest paid over the loan's life is typically higher, since the balance being charged interest never reduces.
What counts as a credible repayment vehicle?
Commonly an investment portfolio, pension lump sum, ISA, or a planned property sale — each lender sets its own acceptable list and evidence requirements.
Does switching from interest-only to repayment mid-term reset my amortization?
It restructures your remaining payments to start clearing principal from that point forward — your lender can model the new schedule based on the remaining balance and term.
Is interest-only more common on buy-to-let than residential mortgages?
Yes, considerably — many BTL mortgages are structured as interest-only by default, since rental income is intended to cover the interest while the property itself (or its sale) is the repayment plan.
Related Tools
Mortgage Calculator · Buy-to-Let Calculator · Remortgage Tool
Educational content, not financial advice. Interest-only eligibility and repayment vehicle requirements vary significantly by lender — confirm your specific options with a licensed UK mortgage adviser. Written by the MortgagePro Global team.