Calculator
Mortgage calculator.
Monthly payments for repayment and interest-only mortgages, the total cost of borrowing, and what a 2% rate rise would do.
Monthly payment
£1,148.44
If rates rise by 2%
£1,585.94
at 7.25%, a useful stress test
Total interest over term
£344,531
Balance still owed at end
£262,500
Rates and thresholds for England and Northern Ireland, checked against gov.uk on 9 September 2026. These calculators are for guidance only and are not tax, legal or financial advice. Your own position may differ; confirm figures with your accountant, solicitor or lender before relying on them.
How to read the results
The monthly payment is the number most people look at, but for an investment property the important figures are the total interest over the term and the stress-tested payment. Buy-to-let lenders assess affordability on rent rather than salary, and they test the rent against the interest at a notional rate that is usually higher than the pay rate. If the rent does not cover the stressed interest by the lender’s margin, the loan size is cut.
Interest only or repayment?
Most buy-to-let, HMO and serviced accommodation mortgages are interest only. The monthly cost is lower, mortgage interest is treated differently for tax depending on whether you own personally or through a company, and the capital is repaid on sale or refinance. The trade-off is that the debt does not shrink, so the exit plan matters. Repayment mortgages build equity but reduce monthly cash flow, and for HMOs in particular the difference can be several hundred pounds a month.
What the calculator does not include
Arrangement and valuation fees, early repayment charges, product transfer costs and the difference between the pay rate and the lender’s reversion rate at the end of a fixed period. For a full view of a deal use the rental yield calculator alongside this one.
Want a second pair of eyes on the numbers?
A free 15-minute call is often enough to spot the thing the calculator cannot: the licensing issue, the lender that will not like the property, the tax angle you had not considered.