Interest-Only vs Repayment Calculator
Compare the monthly payment on interest-only against a standard repayment mortgage, and the total-cost truth: interest-only feels cheaper every month, but you still owe the full balance at the end.
Not financial advice. This is an estimate, representative figures, not financial advice. Actual mortgage terms, lender policies on interest-only switches, and your Mortgage Charter eligibility may differ. If you're worried about affording your mortgage, free, independent help is available from MoneyHelper (moneyhelper.org.uk) and StepChange (stepchange.org).
Enter your mortgage balance, rate and term
The monthly payment and total cost on interest-only vs repayment appear here as you type.
How this comparison is calculated
The repayment monthly payment uses the standard mortgage annuity formula, a level payment that clears both interest and principal over the term. The interest-only monthly payment is simply the balance multiplied by the monthly interest rate, since none of the balance is ever repaid, this payment stays exactly the same every month, and the total interest is just that payment multiplied by the number of months. The temporary-switch scenario assumes N months of interest-only from the start of the mortgage (the balance doesn't move during that time), then a new, higher repayment amount recalculated over the shortened remaining term so the mortgage still clears on the original end date, the extra interest this causes is the difference between that total and a standard, unbroken repayment mortgage over the same overall term.