Mortgage Stress Test Calculator
Find your breaking point rate — the interest rate at which your bond becomes unaffordable. See if you can survive a +1%, +2%, +3% or +4% rate increase.
Rate Stress Scenarios
How your financial position changes at different interest rate levels. Disposable income = gross income minus expenses minus bond payment.
| Scenario | Rate | Monthly Payment | Disposable Income | Status |
|---|---|---|---|---|
| Current rate | 10.3% | R 12 369/mo | R 17 631 | Safe |
| +1% | 11.3% | R 13 221/mo | R 16 779 | Safe |
| +2% | 12.3% | R 14 094/mo | R 15 906 | Safe |
| +3% | 13.3% | R 14 987/mo | R 15 013 | Safe |
| +4% | 14.3% | R 15 898/mo | R 14 102 | Safe |
Green = >10% of income remains | Amber = positive but tight | Red = cash-flow negative
Understanding the Mortgage Stress Test How to use • Formula • Example
How to Use This Calculator
Enter your bond amount, current interest rate, remaining term, gross monthly income, and all monthly expenses excluding your bond (food, car, insurance, utilities, credit cards). The calculator shows your disposable income at the current rate and at +1%, +2%, +3% and +4% rate increases, with a traffic-light status for each scenario.
The Bank View tab shows how your lender evaluates your application under the SARB stress test requirement.
The Stress Test Formula
Where the stressed bond payment is recalculated at the current rate plus the rate increase scenario.
- Green (Safe) — disposable income exceeds 10% of gross income
- Amber (Caution) — positive disposable income but below 10% buffer
- Red (At Risk) — disposable income is negative; you cannot cover costs
Worked Example
Nomsa has a R1,260,000 bond at 10.25% over 20 years. Her gross income is R45,000/month and non-bond expenses are R15,000/month.
Her current bond payment is approximately R12,437/month. Disposable income: R45,000 − R15,000 − R12,437 = R17,563 (Green).
At +2% (rate goes to 12.25%), her payment rises to approximately R13,857/month. Disposable drops to R16,143 — still Green, but the impact is R1,420/month more in bond costs.
Her breaking point would be approximately at 24.25% — unlikely in the short term, giving her a strong buffer against rate increases.
Frequently Asked Questions
What is a mortgage stress test in South Africa?
A mortgage stress test evaluates whether you can still afford your bond repayments if interest rates rise. South African banks are required by the SARB Prudential Standard PA 001 to assess applicants at a minimum of 200 basis points (2%) above the contracted rate. The goal is to ensure borrowers are not over-exposed to rate increases, which protects both the borrower and the financial system.
How much do interest rates typically rise in South Africa?
The SARB MPC meets every two months and typically adjusts the repo rate in increments of 25 basis points (0.25%). During the 2021–2023 hiking cycle, South Africa raised rates by a cumulative 475 basis points (4.75%) over two years. The standard bank stress test of +2% represents roughly 8 rate hikes, which is realistic over a 3-5 year period. Planning for a +3% to +4% scenario provides a more conservative buffer.
What DTI ratio does SARB require banks to use for stress testing?
The SARB requires banks to stress test at current rate plus at least 200 bps (2%). Most SA banks apply a maximum debt-to-income (DTI) ratio of 28–33% of gross monthly income. Under the NCA, the guideline is 30%. At the stressed rate, your bond payment divided by gross income should remain below the bank's DTI threshold for the application to be approved.
What is a "breaking point" rate?
Your breaking point rate is the interest rate at which your bond payment plus living expenses exceed your gross income, leaving you with negative disposable income. It is the rate at which you would technically default unless you cut spending or receive additional income. The further your breaking point is above the current rate, the more resilient your financial position is to rate hikes.
How can I improve my stress test results?
To push your breaking point higher and improve your stress test results: reduce your bond amount by making a larger deposit; increase your income through side income or bonuses; cut monthly expenses such as subscription services, club memberships, or high car instalments; or consider a shorter bond term (though this raises current payments, you build equity faster and your balance declines more quickly). An access bond with an offset facility also helps by letting you reduce the effective balance when rates rise.