Loan Interest Calculator
The UK's easy loan interest calculator. Enter the amount, interest rate (APR) and term to get your monthly repayment, total interest and repayment schedule instantly. No sign-up.
Enter the loan details
How the loan interest calculator works
The calculator uses the annuity (amortisation) formula, the same method UK lenders use to work out fixed monthly repayments on a personal loan or car loan. Each month you pay the same amount; at first most of it is interest, and as the balance falls more of it repays the capital.
The monthly payment is worked out as M = P × r × (1+r)n / ((1+r)n − 1), where P is the amount borrowed, r is the monthly interest rate (the annual rate divided by 12) and n is the number of monthly payments.
What APR means
The APR (Annual Percentage Rate) includes the interest plus any compulsory fees, so it reflects the true yearly cost of a loan. The representative APR is the rate at least 51% of accepted borrowers receive – your own rate can be higher depending on your credit history.
Example: a £10,000 loan at a 6% nominal rate with a £100 arrangement fee and a £5/month account fee over 5 years has a higher APR than 6%, because the fees add to the cost.
Tips for choosing a loan
- Compare the total amount repayable, not just the monthly payment – a longer term lowers the monthly cost but usually raises the total interest.
- Check for an arrangement fee or early repayment charge before you sign.
- Overpaying, even a little, can cut the total interest and clear the loan sooner.
- Always compare the representative APR across lenders on a like-for-like basis.
Frequently asked questions – Loan Interest Calculator
It changes with the Bank of England base rate and your credit profile. In 2026, a competitive personal loan rate is broadly in the mid-to-high single digits for well-rated borrowers, while smaller loans and those for people with thin credit files cost more. Always compare the representative APR.
Yes. An overpayment reduces the outstanding balance, so less interest builds up afterwards and the loan finishes sooner. Check whether your agreement has an early repayment charge first – many personal loans allow penalty-free overpayments up to a limit.
Usually yes. During a payment holiday interest still accrues and is added to the balance, so the total cost rises. Use it only when you need to.
It will be very close. A lender's final figure can differ by a few pounds because of rounding, the exact day count, or fees specific to your agreement. Use this as an indicative comparison and rely on the lender's written quotation for the exact numbers.