Loan Calculator
Calculate monthly payments, total interest, and see the full amortisation schedule.
Repayment Summary
Frequently Asked Questions
How Loan Repayments Are Calculated
Most loans in the UK use a fixed repayment structure, where you pay the same amount every month for the entire term. Each payment covers some interest and some principal (the amount you actually borrowed). Early in the loan, most of your payment goes towards interest; later, most goes towards principal.
The Formula
Monthly payment M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1], where P is the loan amount, r is the monthly interest rate (annual rate ÷ 12 ÷ 100), and n is the total number of monthly payments.
Worked Example: £200,000 Mortgage at 4.5% Over 25 Years
Monthly payment: £1,111.50. Total repaid over 25 years: £333,450. Total interest: £133,450 — that's 66.7% of the original loan amount paid in interest alone. This is why even small rate differences matter enormously over a long term.
How Interest Rate Affects Your Payments
On a £200,000 mortgage over 25 years: at 3% you pay £948/month (£84,478 total interest). At 4.5% you pay £1,112/month (£133,450 total interest). At 6% you pay £1,289/month (£186,653 total interest). The difference between 3% and 6% is £341/month — or £102,175 over the full term.
Overpayments
Making overpayments can dramatically reduce the total interest you pay. Even an extra £100/month on a £200,000 mortgage at 4.5% can save over £25,000 in interest and reduce your term by several years.
Related Calculators
Use the salary calculator to work out your monthly take home pay and see what you can afford. The compound interest calculator shows the flip side — how savings grow. The percentage calculator helps compare interest rates.
KwikSum's loan and mortgage calculator shows your monthly repayment, total amount repaid, total interest paid, and a full year-by-year amortisation schedule. Works for any loan: mortgages, personal loans, car finance, or any fixed-term borrowing.