A South African home loan — a “bond” — is a standard amortising loan, but its rate is usually variable and linked to the prime lending rate. This calculator produces your monthly repayment, total interest over the term, and a stress test at a higher rate so you can judge affordability the way a bank does.
Rate note: the prime lending rate moves with the SARB repo rate, so the ~11.75% figure used here is a reference point, not a fixed value. Enter the rate your bank actually quotes (usually prime ± a margin) and confirm the current prime rate with the South African Reserve Bank before relying on a repayment figure.
How the bond repayment is calculated
The monthly repayment uses the amortising-loan formula:
P = price − deposit (loan amount)
r = annualRate / 100 / 12 (monthly rate)
n = years × 12 (number of payments)
M = P · r · (1 + r)^n / ((1 + r)^n − 1)If the rate is 0, the payment is simply P / n. Total interest is M · n − P. The
stress test repeats the calculation at annualRate + 2% to show how a prime
increase would affect you.
Worked example
A 1,500,000 ZAR property with a 150,000 deposit gives a 1,350,000 loan. At 11.75% over 20 years (240 payments) the monthly repayment is about 14,629 ZAR, with total interest near 2.16 million over the life of the bond. Because the rate is variable, always check the stress-test figure: at 13.75% the same bond costs roughly 16,442 a month. A larger deposit cuts both the payment and the total interest substantially.
South Africa bond costs to budget beyond the repayment
Monthly bond repayments are only part of homeownership cost in South Africa. Budget separately for these items:
- Transfer duty. Payable to SARS on most property purchases on a sliding scale starting above R1.1 million. Use the Transfer Duty calculator to estimate this before you commit to a purchase.
- Bond registration fees. The conveyancing attorney registering the bond charges a fee based on the loan amount — typically a few thousand rand for a standard residential bond.
- Conveyancing (transfer) attorney fees. Separate from bond registration; the transfer attorney’s fee scales with the purchase price.
- Homeowners insurance. Banks require this as a condition of the bond; premiums vary by property value and location.
- Rates and levies. Municipal rates are charged annually by the local authority based on the property’s market value. For sectional title, monthly levies to the body corporate cover building insurance and shared maintenance.
As a rough rule of thumb, budget an additional 1.5% to 2.5% of the property’s value per year for rates, insurance, levies, and maintenance combined, on top of bond repayments.
Variable rate risk: why the stress test matters
South African home loan rates move with prime, and prime has moved by 3 to 4 percentage points in a single rate cycle historically. On a R1.35m bond the difference between 11.75% and 13.75% is roughly R1,800 per month in additional repayment. Always check that your budget can absorb a 2-point rise before committing. The stress-test output in this calculator shows your payment at that higher rate so you can confirm affordability before signing.
How the deposit changes the whole picture
Because interest compounds on the outstanding balance for up to 20 years, the deposit you put down affects far more than the loan amount — it changes the monthly payment, the total interest, and often the rate the bank offers:
| Deposit on a R1.5m home | Loan | Monthly @ 11.75%/20yr | Total interest |
|---|---|---|---|
| 0% (100% bond) | R1,500,000 | ~R16,255 | ~R2.40m |
| 10% (R150,000) | R1,350,000 | ~R14,629 | ~R2.16m |
| 20% (R300,000) | R1,200,000 | ~R13,004 | ~R1.92m |
A 20% deposit here cuts roughly R480,000 off the lifetime interest versus a 100% bond, on top of usually earning a better rate — which is why banks reserve their sharpest pricing for lower-LTV applications.
A quick pre-approval sanity check
Before approaching a bank, run the instalment this tool produces against the affordability screen South African lenders apply: the National Credit Act obliges lenders to assess that the instalment fits your overall debt position and living expenses, not just your gross salary — a bond repayment much above roughly 30% of gross monthly income is where most applications start to strain. If the calculated repayment sits above that line, test a longer tenure, a larger deposit, or a lower price band before applying — a declined application costs you time and leaves a credit-record footprint, while a recalculated one costs nothing.
Sources
- South African Reserve Bank — Selected interest rates (repo and prime) — the prime rate this tool references.
- SARS — Transfer Duty — the purchase-time duty to budget alongside the bond.
This is a planning estimate; confirm the rate and all fees with your bank.