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How to use the Car Affordability calculator
Car Affordability answers the question both ways: what car your income can carry, or what you would need to earn for a car you want. It runs three well-known rules at once, because affordability is a range, and the spread between the strict rule and the loose one is the honest answer.
The tool works in two directions. From income, it shows the price each rule says you can afford. From a car price, it shows the income each rule says you need. It runs three rules together: a payment cap on your take-home pay, the 20/4/10 rule, and the strict 1/10th rule.
Running costs are where car budgets break, and most calculators ignore them. Fuel, insurance and upkeep can rival the instalment, and this tool counts them in the all-in transport ceiling. The result is often sobering, which is the point.
What you'll need
- The direction: from your income, or from a car's price.
- Your take-home pay and your income before tax. The payment cap works on take-home; 20/4/10 and 1/10th are written against gross.
- The finance: new or used, term, deposit, any balloon, and a rate (pick your credit band and it fills in).
- Your running costs, fuel, insurance and upkeep, entered once on the Running costs card and shared across the Auto tools.
How to use it
Pick the direction and the rule. From income, enter your take-home and gross pay; from a car price, enter the price. Then set the finance: term, deposit, credit band and rate.
Fill in the Running costs card honestly, because those costs count toward the ceilings. The three rules sit side by side in a chart, so you can see how far apart they are.
Reading your result
The big number is the answer for the rule you picked: a car price, or an income. The chart shows all three rules together, so you can read affordability as the range it really is. A transport-share card grades the instalment plus running costs against the 20% all-in ceiling.
The payment cap keeps the instalment under 15% of take-home for a new car, 10% for a used one, and the whole transport bill under 20%. 20/4/10 means 20% down, 48 months at most, all car costs under 10% of gross. The 1/10th rule caps the cash price at a tenth of a year's gross income.
A worked example
From a car price: an R400,000 car on a 72-month deal at 12% with R40,000 down, and running costs of about R4,800 a month.
The instalment works out to R7,107. Under the 15% payment cap alone you would need about R47,380 take-home a month. But once the R4,800 of running costs count toward the 20% all-in ceiling, the figure the tool reports is about R59,533. Run it the other way, on an R35,000 take-home, and those same running costs leave only R2,200 a month for an instalment, about an R149,000 car. The running costs, not the rate, are doing the work.
What it does not do
These are guidance rules, not a lender's decision. Bank Affordability runs the legal NCA test, and Finance & Balloon prices an exact deal. The 1/10th rule reads brutally strict on purpose, as a wealth-builder benchmark rather than the norm. It is information, not advice.
To price a specific deal in full, including the balloon trap, use Finance & Balloon. To see where the car sits in your monthly budget, use Budget Splits. When you are ready, open Car Affordability.
Money Cat is an information tool, not financial advice. Rates shown reflect SA prime as at June 2026. Confirm any quote with the lender.