How Banks Calculate Home Loan Affordability (And Why It’s Not Just Maths)
One of the most confusing parts of buying a home is affordability. Many buyers assume banks simply look at their salary, apply a formula, and approve a loan based on the result.
In reality, home loan affordability is about long-term sustainability, not just income. This article explains how banks calculate affordability in South Africa, what they include and why two people earning the same amount can receive very different outcomes.
Affordability is about whether a home loan remains manageable over time. Even when interest rates or personal circumstances change.
What “affordability” really means to banks
Affordability is a measure of how comfortably you can repay a home loan after all your other financial commitments are taken into account.
Banks are not asking:
“Can you pay this today?”
They are asking:
“Can you still pay this if rates increase, expenses rise or income fluctuates?”
That difference matters.
What banks include in an affordability calculation
Banks look at more than just your salary. Typical inputs include:
- Gross and net income
- Regular monthly expenses
- Existing debt repayments
- Living costs (even if not declared in detail)
- Estimated bond repayment at stressed interest rates
This is why affordability outcomes can feel conservative. Banks build in buffers to reduce risk.
Why income alone is not enough
Two buyers earning the same salary can receive very different affordability results. That’s because banks consider:
- How much of your income already goes toward debt
- Whether expenses are realistic for your lifestyle
- How stable your income is over time
This is also why buyers are sometimes approved for less than they expected, even with good credit behaviour.
How interest rate stress testing affects affordability
Banks don’t calculate repayments at today’s interest rate alone.
They apply a stress test, meaning:
- Repayments are calculated at a higher rate
- Affordability must still work under that scenario
This protects both the bank and the buyer from future rate increases.
Common affordability mistakes buyers make
Many affordability problems are avoidable. Common mistakes include:
- Under-declaring expenses
- Assuming bonuses or overtime will always count
- Taking on new debt before final approval
- Using online calculators without understanding bank rules
Understanding how affordability works early can prevent disappointment later in the process.
How affordability links to pre-approval and declines
Affordability plays a role at every stage of the home loan process. It affects:
- Home loan pre-approval amounts
- Whether final approval is granted
- Why some applications are declined despite good credit
This is why affordability is often the hidden reason behind a home loan decline.
What you can do to improve affordability
Improving affordability doesn’t always mean earning more. Depending on your situation, it may involve:
- Reducing short-term or revolving debt
- Adjusting the purchase price
- Increasing a deposit
- Allowing time for expenses to stabilise
- Understanding how repayments change over loan terms
Using a bond repayment calculator can help you test scenarios realistically before applying.
Unsure what banks will really consider affordable for you?
If you’d like clarity before applying, you can WhatsApp me your details and I’ll explain how affordability is likely to be assessed. Calmly and honestly.
FAQ
How much of my income can go toward a home loan?
Banks prefer this to be below 30% of your gross income, but there is no fixed percentage. Banks assess affordability based on overall risk, expenses and income stability rather than a single ratio.
Do banks use my exact expenses?
Banks use declared expenses but also apply minimum living cost estimates to ensure repayments remain sustainable.
Can home loan affordability change after pre-approval?
Yes. New debt, lifestyle changes or updated expense information can affect final affordability.
Does a larger deposit improve affordability?
A deposit can reduce repayments and risk, which may improve your home loan affordability in some cases.
