Loan & Installment Calculator
Monthly payment, total cost and the real annual rate — for reducing-balance and flat-rate finance.
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Runs entirely in your browser. Nothing you enter is uploaded or stored on a server.
About this tool
Most installment calculators give you a payment and stay silent on the question that matters: what does the finance actually cost? Lenders advertise a flat rate in one place and an annual rate in another, and the two numbers are not comparable. This calculator works both ways and always shows the real annual rate — the only figure you can hold two offers against.
How to use
- 1Pick the method: reducing balance if interest is charged on what you still owe, flat rate if it is charged on the full amount.
- 2Enter the finance amount.
- 3Enter the annual rate as the lender advertised it.
- 4Enter the term and choose years or months.
- 5Read the monthly payment and total interest, and on a flat rate compare the advertised rate with the real one.
When you need it
- Comparing two offers where one quotes a flat rate and the other an annual rate.
- Knowing the monthly payment before applying for a mortgage or car finance.
- Pricing an installment plan you offer to your own customers.
- Checking that a payment a lender quoted matches the amount and term you agreed.
Frequently asked questions
What is the difference between a flat rate and reducing balance?
On reducing balance, interest is charged each month on what is left of the loan, so it falls with every payment. On a flat rate it is charged on the original amount for the whole term no matter how much you have repaid. At the same quoted number the flat rate costs far more — often close to double.
Why is the real rate higher than the rate I entered?
Because you chose the flat rate method. The real rate is the reducing-balance equivalent, which is what you can compare against an offer quoted as an annual rate. A 5% flat rate over five years works out near 9% a year.
Does the result include fees and insurance?
No. It covers principal and interest only. Arrangement fees and insurance sit on top, so ask for the total amount payable rather than the rate alone.
What is the monthly payment on 100,000 over five years?
At 5% reducing balance the payment is about 1,887 and total interest about 13,227. At 5% flat the payment is 2,083 and total interest 25,000 — nearly twice the cost for the same quoted number.
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