How the loan repayment calculator works
Last updated 10 November 2026
A loan is paid back in monthly instalments. Each instalment pays that month’s interest first, and what is left reduces the amount you still owe, which is called the capital. This calculator has two modes: an instalment loan with a fixed term, such as a personal loan, and a credit card or other revolving balance where you choose a fixed monthly payment.
How it works
- Interest: the yearly rate divided by 12 is charged each month on the balance you still owe.
- Instalment: the level monthly amount that clears the loan exactly by the end of the term. With a 0% rate it is simply the loan divided by the number of months.
- Fees you enter: an initiation fee and a monthly service fee. They are your own inputs, taken from your quote. The initiation fee is either added to the loan, so it earns interest, or paid upfront. The monthly service fee is charged every month the loan runs and is added to the payment you see.
- Extra payment: an amount paid on top of the instalment each month. It goes to the capital, so less interest builds up and the loan ends sooner.
- Credit card mode: the calculator adds a month of interest, takes off your payment, and repeats until the balance is zero. It assumes no new spending and no other fees.
Worked example
Take a loan of R 50 000 at 18% a year over 36 months. These are the starting values on the page, so replace them with your own quote.
- The monthly instalment is R 1 807.62.
- Over 36 months you repay R 65 074, of which R 15 074 is interest.
- Say the quote also shows a R 1 000 initiation fee and a R 60 monthly service fee. If the initiation fee is added to the loan, the instalment becomes R 1 843.77 and the payment with the service fee is R 1 903.77. Total fees are R 3 160, and you repay R 68 536 in all.
- If the same R 1 000 fee is paid upfront instead, the instalment stays R 1 807.62. You repay R 68 234 in all, which is R 301 less, because the fee earns no interest.
- Pay R 500 extra a month and the loan is cleared in 2 years 3 months instead of 3 years, saving R 4 149 in interest.
- For a credit card balance of R 15 000 at 21% a year, the interest added in the first month is R 262.50. A payment of R 600.00 a month clears it in 2 years 10 months, with R 4 900 in interest.
How to read your result
The headline for a loan is the monthly payment: the instalment plus any monthly service fee. Total interest is what borrowing costs on top of the amount you receive. Total fees adds the initiation fee and every monthly service fee. Total you repay is the amount borrowed, the interest and the fees together.
Early on, most of each instalment is interest. In the first month of the example loan the interest is R 750.00, so the capital falls by much less than the instalment. The split shifts towards capital as the balance falls, which is why extra payments made early save the most.
For a credit card, the key figure is the interest added in the first month. A payment equal to that amount, such as R 262.50 on R 15 000 at 21%, leaves the balance exactly where it was, so it is never paid off. A payment below it lets the balance grow. The calculator shows a warning in both cases.
Check the limits and the true cost
The National Credit Act sets limits on interest rates and fees for different types of credit. This page does not state them. To compare a rate with the legal formula, use the interest rate limit checker. To turn fees and repayments into one yearly rate, use the loan fee and true cost checker.
Things to watch
- This is an estimate from the figures you type in. Your lender’s quote and credit agreement decide the actual instalment, fees and total.
- A variable rate can change during the loan, which changes the instalment. The calculator keeps the rate you enter the same for the whole term.
- Credit life insurance, other add-on costs and interest charged daily are not included unless you enter them as fees.
- Extra payments only shorten a loan if the lender puts them toward the capital. Check your agreement for any fee on early settlement.
- For a home loan or a vehicle loan, see the bond repayment calculator or the car finance calculator. To plan paying off several debts together, see the debt payoff planner.
The calculator gives facts about your numbers, not advice. See the disclaimer.