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How to use the Bond Repayments calculator
The Bond Repayments calculator shows what a home loan really costs and how much an extra payment saves. It runs two bonds side by side, so you can pit a plan against a plan: a bigger deposit, a shorter term, an extra R2,000 a month, and watch the interest and the years fall away.
Most bond calculators give you one monthly number and stop. This one runs the full schedule for two scenarios at once, so the comparison is the point. It shows the total interest, the payoff month and the true price of each, and it charts the balance and the interest as they unwind.
The lesson it teaches fastest is the power of paying extra. On a normal SA bond, a few thousand rand more a month can cut years off the term and hundreds of thousands off the interest, because every extra rand goes straight at the principal.
What you'll need
- For each scenario: the price, deposit, interest rate and term. Prime is 10.5% as at June 2026.
- Any extra monthly payment, and any once-off lump sum with the month it lands.
- For the debt-load gauge at the bottom, your take-home pay and your other monthly debt.
How to use it
Set Scenario A as your base case. Then change one thing in Scenario B: a bigger deposit, a shorter term, or an extra monthly amount. The defaults already pit a plain bond against the same bond with R2,000 extra a month, which is the comparison worth seeing first.
Add a lump sum, like a bonus or a tax refund, and set the month it arrives, to see what one payment does. Lower down, enter your take-home pay and other debt to read your repayment as a share of income against the national average.
Reading your result
The three stat cards compare the two scenarios: the interest saved going from A to B, and each scenario's monthly payment, payoff time and total interest. The true-price strip shows what you actually hand over, deposit and principal and every rand of interest, against the purchase price.
The charts do the rest. Bond balance over time shows B falling away sooner; the principal-versus-interest chart shows how much of each early payment is pure interest; and the cumulative-interest chart shows the gap that is the money you keep. The schedule table breaks it down year by year, and each year unfolds into months.
A worked example
An R1,800,000 bond (an R2,000,000 home with 10% down) at 10.5% over 20 years. Scenario A pays the required amount; Scenario B adds R2,000 a month.
| Scenario A | Scenario B, +R2,000 | |
|---|---|---|
| Monthly payment | R17,971 | R19,971 |
| Total interest | R2,513,001 | R1,762,885 |
| Paid off in | 240 months | 179 months |
The extra R2,000 a month saves R750,116 in interest and clears the bond 61 months early, just over five years sooner. You spend R2,000 more a month and get back five years and three quarters of a million rand. The case for paying extra, in two columns.
What it does not do
It assumes a fixed rate for the whole term, and real SA bonds track prime, which moves. To see what a rate change would do, use the Rate Shock tool. The schedule is an estimate; your bank's rounding and fees will differ slightly.
For the why behind the rate, read what a 1% repo move does to your bond. To stress-test a rate rise, use Rate Shock. When you are ready, open Bond Repayments.
Money Cat is an information tool, not financial advice. The rate shown is the SARB prime as at June 2026; your quoted rate will differ. Confirm with your bank.