How the bond repayment calculator works
Last updated 9 November 2026
A bond is a home loan. You borrow the purchase price less your deposit, and pay it back in equal monthly instalments over a fixed term, usually 20 years. Each instalment covers that month’s interest first. Whatever is left pays off some of the loan itself, which is called the capital.
The calculator takes your purchase price, subtracts your deposit to get the loan amount, and works out the level instalment that clears the loan exactly by the end of the term. Interest is worked out monthly: the yearly rate divided by 12, charged on the balance you still owe.
If you add an extra monthly payment, the calculator runs your bond month by month. The extra goes straight to the capital, so the balance falls faster, less interest builds up, and the bond is paid off early. It then compares that with the normal schedule to show the time and interest you save.
Worked example
Say you buy a home for R 1 500 000 and put down a 10% deposit of R 150 000. These are the calculator’s starting values.
- Your bond is R 1 500 000 − R 150 000 = R 1 350 000.
- At the prime rate of 10.75% over 20 years, the monthly repayment is R 13 705.59.
- Over the full term you pay R 1 939 342 in interest, so the home costs R 3 289 342 in repayments, plus your deposit.
- In the first year, R 144 143 of your repayments goes to interest and only R 20 324 to capital.
- Pay R 1 000 extra a month and the bond is paid off in 16 years 2 months, saving about R 439 753 in interest.
The rate matters a lot. At 11.75%, one percentage point above prime, the same bond costs R 14 630.05 a month, which is R 924 more.
What the figures mean
- Monthly repayment is the fixed instalment that pays off the bond over the term, if the rate stays the same.
- The prime rate is the rate banks use as a starting point for home loans. It moves with the Reserve Bank’s repo rate, which is now 7.25%. Your bank may offer you prime, or a rate above or below it, based on your credit record, income and deposit.
- Total interest is everything you pay on top of the loan amount over the full term. On a long bond it can be more than the loan itself.
- Capital is the part of each payment that reduces what you owe. Early on most of your payment is interest. The split shifts towards capital as the balance falls.
- Time and interest saved show what an extra monthly payment does compared with paying only the normal instalment.
Things to watch
- Most South African bonds have a variable rate linked to prime. When the Reserve Bank changes the repo rate, your repayment changes too. The next decision is on 19 November 2026.
- This repayment does not include bond insurance, home insurance, rates and taxes, levies, or a monthly bank service fee. Your bank’s quote shows those.
- Upfront costs come on top of the deposit: transfer duty, attorney fees and Deeds Office fees. Work out the duty with the transfer duty calculator, and check what you could borrow with the bond affordability calculator.
- Extra payments only help if they stay in the bond. If your bond lets you take them back out (an access bond), withdrawing them undoes the saving.
Sources
The prime rate of 10.75% and repo rate of 7.25% apply from 25 September 2026. The calculator uses the standard instalment formula with interest compounded monthly. All figures were last checked on 9 November 2026, and the full list of sources is at the bottom of this page.