Mortgage Repayment Calculator

What does this calculator assume?

• A single fixed interest rate for the whole term — most UK mortgages re-fix every 2–5 years, so your rate (and payments) will change.
• Standard monthly repayments — no overpayments, payment holidays, or rate changes.
• Doesn't include arrangement fees, valuation, conveyancing, stamp duty, or insurance.
• Doesn't factor in early repayment charges (ERCs) during fixed-rate periods.
• Doesn't run an affordability check — what a lender will actually offer can be lower.

Why does the interest portion change over time?

Your monthly payment stays the same throughout the term, but interest is calculated each month on the remaining loan balance. As the balance falls, less of each payment goes to interest and more chips away at the loan itself — which is why the year-by-year breakdown shows interest dominating in early years and principal dominating in later years.

What's the difference between repayment and interest-only?

With a repayment mortgage, your monthly payments cover both interest and a portion of the loan, so it's fully paid off by the end of the term. With interest-only, you only pay the interest each month — the original balance stays the same and must be repaid separately at the end.

Interest-only is uncommon on residential mortgages and usually requires evidence of a repayment vehicle (savings, investments, or sale of the property).

Why does my actual mortgage quote look different?

Real quotes include things this calculator doesn't: arrangement fees, the lender's affordability assessment, and the actual rate available to you — which depends on your deposit, credit profile, and the lender's current pricing.

Most UK mortgages also re-fix every 2–5 years rather than staying at one rate for 25, so your payments will change over the life of the loan.

What happens if interest rates change?

When your fixed deal ends and you remortgage onto a higher rate, your payments go up; the reverse is true if rates fall. Our overpayment calculator shows the impact of paying extra now and can help you build a buffer before any rate change.