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How to use the Rate Shock calculator
Rate Shock stress-tests your bond against a rate rise before the Reserve Bank hands you one. You set how far rates move against you, and it re-prices your repayment, shows the extra over the term, and measures the new payment against your income.
Almost every SA home loan tracks prime, so when the repo rate rises your repayment rises a few weeks later. This tool asks the question banks ask before they lend: if rates climb two or three points, can you still pay? It re-prices the bond on the same remaining term, the way banks adjust.
Buy at the very top of your budget and one rate cycle can break you. The 2022 to 2023 cycle added 4.75 points in 20 months. Testing plus two or three points is not pessimism, it is what recently happened, and the time to find out is before you sign.
What you'll need
- Your outstanding balance, current rate and remaining term.
- Your monthly income, for the share-of-income gauge.
- The size of the shock to test, in percentage points.
How to use it
Enter your bond, then your monthly income so the tool can show the new payment as a share of it. Banks stress-test around 30%.
Drag the shock slider to the rise you want to test. Plus two points is a sensible starting stress; the slider also goes negative, to see what a cut would save. The tool shows the rate your bond would sit at after the move.
Reading your result
The headline is your repayment after the shock, with the rand increase against today's payment. The share-of-income gauge grades it: comfortable under 30%, stretched past it. The extra-over-the-term figure is what the higher rate costs if it stays.
The rate-range chart plots your payment at every shock from minus two to plus four points, with today and your chosen shock marked. The cumulative chart stacks the extra cost up month after month.
A worked example
An R1,500,000 balance at 10.5% with 20 years left, on a R60,000 monthly income, tested with a two-point rise.
Today's payment is R14,976. At 12.5% it becomes R17,042, which is R2,066 more a month and R495,938 over the remaining term. It takes the bond to 28.4% of income, still inside the 30% banks look for, but only just. A third point would push it past comfortable.
What it does not do
It holds the term fixed, which is how banks usually adjust, though some let you extend the term instead to soften the blow. It does not predict rates; it shows what a move you choose would cost. It is information, not advice.
For why the repo rate moves your payment, read what a 1% repo move does to your bond. To test extra payments against the rise, use Bond Repayments. When you are ready, open Rate Shock.
Money Cat is an information tool, not financial advice. The current rate shown is the SARB prime as at June 2026. Confirm your own rate with your bank.