Interest-Only Mortgage Calculator
Calculate your monthly interest-only payment and total interest over the term — and see clearly how much capital remains owed at the end.
Enter your loan amount, the annual interest rate, and the term in years. The calculator shows your monthly interest payment (which stays fixed as the capital never reduces), the total interest paid over the full term, and — critically — the full loan amount that will still be owed when the term ends.
To evaluate how these commitments align against standard principal amortization paths, analyze your financing choices with our Mortgage Repayment Calculator.
An interest-only mortgage is a lending agreement where your monthly outgoings satisfy solely the raw interest accrued on your loan principal. None of your regular cash inputs are directed toward decreasing the baseline debt balance. Because your total principal remains completely static across the lifespan of the loan, your ongoing interest fees remain identical month-over-month unless your underlying mortgage deal tier or tracking rate shifts.
At the formal conclusion of the term, the entire original borrowing principal must be paid back to the financial institution. Homeowners utilizing this structure must maintain a viable repayment vehicle to clean up the debt liability down the road. Standard approaches include ISA wrappers, general investment allocations, pension capital options, or down-scaling your location by selling the property.
On a £200,000 mortgage at 5% over 25 years:
The interest-only strategy generates nearly £100,000 in additional lifetime interest overhead — all while leaving your fundamental debt principal entirely intact. You can track this exact pace of debt decay and interest accrual across structural timelines by mapping your numbers inside the Mortgage Amortization Calculator.
A common pitfalls for borrowers is focusing exclusively on minimal monthly costs while ignoring long-term capital liabilities. This application breaks out your ending balance figures clearly rather than burying them in footnotes. Misjudging or failing to build a robust principal settlement strategy is one of the single biggest drivers of modern property refinancing friction in the UK.
The monthly payment on an interest-only structure is calculated using a simple interest formula: Loan Amount × (Annual Interest Rate ÷ 12). For example, a £200,000 loan balance at a 5% interest rate results in an ongoing monthly liability of £833.33. Because your capital principal never reduces over time, this payment amount remains perfectly static unless your underlying interest rate fluctuates.
The entire original loan balance remains fully outstanding at the end of the mortgage term. Because your monthly payments only satisfy the accumulating interest debt, you must repay the full capital amount borrowed in a lump sum. This is typically achieved via specialized repayment vehicles like ISAs, structural equity portfolios, pension cash allowances, or by selling the underlying property.
Interest-only structures offer lower immediate monthly payments because you are skipping the capital amortization component entirely. However, they cost significantly more over the lifetime of the mortgage. On a £200,000 mortgage at 5% over 25 years, an interest-only structure generates £250,000 in total interest while still leaving you with a £200,000 debt footprint. A standard repayment framework costs more monthly but accumulates only £150,754 in total interest and eliminates the debt entirely.
Yes. Most UK mortgage lenders allow you to overpay up to 10% of your outstanding capital balance annually without triggering early repayment charges. When you overpay on an interest-only mortgage, the funds directly reduce the core debt principal. This immediately drops your baseline calculations, causing your subsequent monthly interest payments to fall. You can evaluate variations in overpayment rules with our Mortgage Overpayment Calculator.
Interest-only structures have a completely linear relationship with interest rates. If your mortgage rate doubles, your monthly commitment doubles exactly. This is structurally distinct from traditional repayment mortgages, where a shifting rate interacts dynamically with an amortizing combination of both principal and interest components over time.