Loan Interest Calculator
Estimate monthly repayment, total repayment, and total interest for a loan using the amount borrowed, annual interest rate, and loan term. This is useful for personal loans, car finance, home improvement borrowing, and general comparison shopping.
This calculator is designed to help you understand both the monthly affordability and the full cost over time. Many borrowers focus only on the monthly payment, but the total interest paid can change significantly depending on the rate and term you choose.
Calculate loan cost
Result explanation
The monthly repayment is the amount you would pay each month if the loan is amortising in the standard way. Total repayment shows the full amount repaid over the entire loan term. Total interest shows how much extra you pay above the original amount borrowed.
Interest as a percentage of the loan can be a useful comparison metric when evaluating different lenders, rates, or loan lengths. It helps you see how much the borrowing really costs relative to the principal.
How it works
This calculator uses the standard amortisation formula for loans repaid monthly. Each repayment includes part interest and part principal, which means the outstanding balance gradually falls over time.
Longer terms usually reduce the monthly payment but increase total interest paid overall. Shorter terms tend to cost more each month but reduce the total borrowing cost.
Worked examples
Example 1: Standard personal loan
Loan: £10,000
Rate: 6.5% per year
Term: 5 years
This produces a manageable monthly payment, but the total interest paid across the full term is what determines the true borrowing cost.
Example 2: Comparing shorter vs longer terms
If you borrow the same amount at the same rate over 3 years instead of 5, the monthly repayment rises, but total interest usually falls. This is why term length is one of the most important factors when comparing loan offers.
When to use this calculator
Use this page when you want a quick estimate of repayment affordability and total loan cost. For comparing the fuller cost of borrowing including fees, use the APR Calculator. For forward growth instead of borrowing cost, use the Compound Interest Calculator or the Savings Calculator.