Last updated 23 September 2026 · Written by Kgothatso Moleke · General information, not financial advice
The short version: what a bank will lend you and what you can afford are two different numbers, and the gap between them is where most financial trouble begins. A lender is testing whether you can pay in an ordinary month. You need to know whether you can pay in a bad one.
Why the 30% rule misleads
The common guidance is that housing should take no more than 30% of income. It is a reasonable starting point and it misleads in three specific ways.
Thirty percent of which income? Gross or take-home changes the answer enormously. On R25,000 gross with R19,000 take-home, 30% is either R7,500 or R5,700 — a R1,800 difference, every month. Always use take-home.
The instalment is not the cost. A bond brings rates and taxes, levies, home insurance, maintenance and the repairs a landlord used to handle. A car brings insurance, fuel, tyres and servicing. Budgeting the instalment alone understates the real commitment substantially, and it is the extras that catch people, not the instalment.
It assumes today’s rate lasts. Most South African bonds are linked to prime, so the instalment you qualified on is not the instalment you will pay for twenty years. A percentage point of rate rises on a R600,000 bond is about R411 a month, and nobody asks your permission first.
A better test: the bad month
Work out the total monthly commitment — instalment plus every associated cost — and then ask whether it survives three things happening at once: the rate rising two percentage points, a R5,000 unexpected expense, and one month of reduced income.
None of those is unusual. Rates moved twice in the last two years, cars and geysers break on their own schedule, and income varies for most people at some point. If the commitment only works when all three stay away, it is not affordable — it is affordable on the condition that nothing happens, which is not a condition life honours.
What the lender is actually checking
The National Credit Act requires a lender to assess affordability before advancing credit, and that assessment is genuine — it is why you must provide payslips and bank statements. But it measures your current, documented position at today’s rate. It cannot price in the raise you were hoping for, the baby arriving, or the fact that your income varies.
So approval is evidence that you can probably pay, not evidence that you should borrow the maximum. Treat the approved amount as a ceiling you deliberately stay below rather than a target to reach.
What the gap is worth
On R19,000 take-home, 30% is R5,700 a month, which at 10.75% over twenty years supports a bond of roughly R561,000. Stretching to 36% is R6,840 and supports about R674,000 — R113,000 more house.
That extra R1,140 a month is the difference between a plan with slack in it and one without. A two-percentage-point rate rise on the larger bond would add about R934 a month — which is most of that margin gone. Take the bigger house and the next rate cycle spends your slack for you.
Five questions before you commit
- What is the total monthly cost, including insurance, rates, levies, fuel and maintenance?
- What does it become if rates rise two percentage points?
- Do I still have an emergency buffer after the deposit and transfer costs?
- What happens if my income drops for three months?
- Am I borrowing the maximum I was offered, or the amount I chose?
Question three catches more people than the rest combined. Emptying your savings into a deposit leaves you owning an asset and holding no buffer, which means the first thing that breaks goes onto credit — and you have just taken on the largest commitment of your life.
The affordability calculator works this out with a deliberate buffer built in, and the rate change calculator shows what a rate move does to the instalment. For the underlying mechanism, see how interest rate changes affect what you pay.
How the figures were worked out: bond capacity calculated at 10.75% over 240 months on the stated instalment, excluding rates, levies, insurance and maintenance. Take-home pay is illustrative. Your own figures will differ.