InstalmentLoans

Personal Loan Calculator

A personal loan calculator turns your loan amount, representative APR and term into a fixed monthly repayment. It also shows the total interest, any arrangement fee and the total cost of credit, so you can compare offers before you borrow.

By the InstalmentLoans Editorial Team · Last updated 2 October 2026

Get an instalment loan quote Check the repayment first

We may receive a commission from lenders or brokers if you take out a loan through a link on this site. This does not affect the amount you repay.

WARNING: Late repayment can cause you serious money problems. For help, go to moneyhelper.org.uk

Enter your numbers and press Calculate. Nothing you type leaves your browser.

How this calculator works

A personal loan is repaid in equal monthly instalments. Each payment covers the interest owed for that month plus a slice of the capital, so the balance falls a little faster every month.

The calculator uses the standard repayment formula:

M = P * r * (1 + r)^n / ((1 + r)^n - 1)

Total interest is the monthly repayment times the number of payments, minus the amount borrowed. An arrangement fee is added to the amount you repay, and the estimated APR shows the yearly cost when that fee is included.

The rate you enter is your own assumption. Lenders set rates from your credit history, loan amount and term, so your actual offer may differ.

Frequently asked questions

How is the monthly repayment calculated?
The calculator uses M = P * r * (1 + r)^n / ((1 + r)^n - 1), where r is the annual rate divided by 12 and then by 100, and n is the number of monthly payments. Each payment covers that month's interest plus part of the capital.
Why does a longer term cost more overall?
A longer term spreads the capital over more months, so each repayment is smaller, but you pay interest for more months. Total interest equals the monthly repayment times the number of payments, minus the amount borrowed.
What rate should I enter?
Use the representative APR from an offer you have received, or a rate you want to test. A representative APR is the rate at least 51% of successful applicants receive, so treat it as an assumption rather than a quote.
Does this calculator include fees?
It has an optional arrangement fee field shown as a percentage of the loan. If you leave it at zero, the tool covers capital and interest only.

Related calculators