A monthly home-loan repayment depends mainly on the loan balance, interest rate and remaining term. A calculator can estimate the scheduled instalment, but it does not prove affordability or approval and may exclude fees, insurance, rates, levies, utilities and maintenance.
Test more than one rate and term, compare the total repayment as well as the monthly figure, and use the exact assumptions in each written lender quotation. A lower instalment can result from a longer term and may produce a materially higher total interest cost.
What determines a monthly home-loan repayment?
For a standard amortising loan, the opening balance, rate, payment frequency and term determine the scheduled principal-and-interest instalment. A lender may also apply product rules, rounding, fees, insurance requirements and rate changes that make its statement differ from a simplified calculator.
The purchase price is not automatically the loan amount. A deposit, approved shortfall, capitalised amount or other transaction detail can change the amount financed.
How the repayment formula works
The standard monthly formula is M = P*r*(1+r)^n / ((1+r)^n - 1), where:
Mis the scheduled monthly principal-and-interest payment;Pis the opening loan principal;ris the monthly interest rate; andnis the number of monthly payments.
If the nominal annual rate is 11%, a simplified monthly rate is 0.11 divided by 12. Real statements can differ because of effective-rate conventions, payment dates, variable-rate changes, fees and rounding. Use the lender’s disclosed terms as the transaction record.
Illustrative repayments on R1,000,000
| Illustrative annual rate | Term | Monthly payment | Total of payments |
|---|---|---|---|
| 10% | 20 years | R9,650.22 | R2,316,051.95 |
| 10% | 30 years | R8,775.72 | R3,159,257.65 |
| 11% | 20 years | R10,321.88 | R2,477,252.14 |
| 11% | 30 years | R9,523.23 | R3,428,364.22 |
| 12% | 20 years | R11,010.86 | R2,642,606.72 |
| 12% | 30 years | R10,286.13 | R3,703,005.35 |
Assumptions: constant nominal annual rate divided by 12, monthly payments, no fees, insurance, rate changes, extra payments or lender-specific rounding. The table shows why the lowest monthly figure is not necessarily the lowest-cost choice.
How an interest-rate change affects the payment
A variable mortgage rate can change when its reference rate changes. The South African Reserve Bank held the policy rate at 7.0% in its July 2026 MPC statement, described the outlook as uncertain and lists the next announcement for 23 September 2026. The policy rate is not the customer’s home-loan rate.
In the R1,000,000, 20-year illustration, moving from 10% to 12% increases the calculated monthly payment from R9,650.22 to R11,010.86, a difference of R1,360.64. Do not treat this scenario as a rate forecast.
Why the loan term changes both payment and cost
Extending the term normally reduces the scheduled instalment because the balance is repaid over more months. If the rate and payment pattern remain unchanged, the borrower pays interest for longer. Shortening the term normally increases the required payment but can reduce total interest.
A term must still fit the provider’s rules, applicant circumstances and property. Use the existing home-loan term guide to compare term risk without assuming that the shortest available term is always appropriate.
Calculate from the loan amount, not only the property price
Start with the accepted purchase price, then record the proposed deposit and the amount the lender is being asked to finance. Do not subtract transaction costs from the loan unless the approved product expressly finances those costs.
A 100% loan generally describes purchase-price finance, not a zero-cash transaction. The 100% home-loan guide separates the loan amount from transfer, bond-registration, moving and property costs.
Repayment is not the complete monthly housing cost
Add municipal rates, levies or HOA charges, utilities, building and contents cover, required life cover where applicable, security, maintenance and a repair reserve. For an investment property, also model vacancy, letting and management costs without assuming full rent every month.
A loan can fit a repayment calculator but remain uncomfortable once the property and household costs are included.
Affordability is more than a calculated instalment
The National Credit Act supports responsible credit granting, and the affordability assessment regulations require relevant financial assessment and authentic applicant information. The credit provider applies the assessment and its current policy.
Use Crescent Capital’s affordability calculator for early planning, then reconcile income, deductions, living expenses, debt repayments and evidence. Never omit an obligation to improve a calculator result.
Compare a rate-and-term scenario table
For each loan amount, calculate at least the quoted rate, one lower scenario for comparison and one or two higher stress scenarios. Test the available terms on the same loan amount. Record the calculation date and whether the rate is fixed, variable, capped or otherwise conditional.
Do not mix assumptions between columns. If one scenario includes fees or insurance, either add them to every scenario or show them separately.
Understand principal and interest over time
Each normal payment includes interest and principal. Early in a long amortising loan, the interest portion is generally larger. As the balance reduces, more of an unchanged payment generally goes toward principal.
Request or generate an amortisation schedule using the actual quotation terms. A total repayment calculated at one rate will become outdated if a variable rate changes.
How extra payments may change the result
An extra amount applied to principal may reduce future interest or shorten the effective repayment period, subject to the agreement, account operation and lender rules. Do not assume that an amount deposited into an access facility is irreversibly applied to principal or that access will always remain available.
Ask the lender how additional funds are allocated, whether the scheduled instalment changes, whether funds can be redrawn and what happens on cancellation or default.
Compare written quotations field by field
Record the loan amount, rate, rate basis, term, repayment, initiation and monthly fees, credit-life or property-insurance requirements, conditions, expiry, linked-account requirements and total cost. Check whether figures are monthly, annual, once-off or estimates.
Use Crescent Capital’s home-loan offer comparison guide. A lower rate or repayment is important, but conditions, term and the total transaction also matter.
Common repayment-calculator mistakes
- using the property price when a deposit changes the loan amount;
- treating the current policy or prime rate as the offered mortgage rate;
- comparing different terms without comparing total repayment;
- ignoring fees, insurance and property costs;
- assuming a variable rate will remain unchanged;
- using gross income as proof of affordability;
- rounding early in a multi-step calculation; and
- calling an estimate a quotation or approval.
Frequently asked questions
How much is the monthly payment on a R1 million home loan?
It depends on the rate, term, fees and loan rules. At a constant illustrative 11% over 20 years, the formula gives R10,321.88 before fees and insurance. This is not a quotation.
Does the repo rate equal my home-loan rate?
No. The policy rate affects broader pricing conditions, but the loan quotation contains the customer’s applicable rate and terms.
Is a 30-year loan cheaper because the payment is lower?
Not necessarily. A longer term may reduce the monthly payment but can increase total interest if the rate and payment pattern remain unchanged.
Does a calculator result mean I qualify?
No. The lender assesses the applicant, affordability, credit information, evidence, product and property.
What costs are normally outside the calculator?
Depending on the tool, fees, insurance, rates, levies, utilities, maintenance, moving, transfer and registration costs may be excluded.
How should I stress-test a variable-rate loan?
Calculate at the quoted rate and higher scenarios, then include the full housing budget and check whether an emergency reserve remains.
Can an extra monthly payment save interest?
It may reduce principal and future interest, subject to the agreement and how the lender allocates the payment. Obtain an updated schedule.
Why does my lender’s figure differ from an online calculator?
The lender may use exact dates, rate conventions, fees, insurance, product rules and rounding that a simplified tool does not include.
Should I choose the offer with the lowest monthly payment?
Not from that field alone. Compare loan amount, rate, term, fees, conditions, total repayment and household sustainability.
What information should I bring to a repayment comparison?
Bring each written quotation, loan amount, rate, term, repayment, fees, conditions and expiry, plus the household’s full monthly property budget.
Turn the estimate into a responsible comparison
A useful repayment calculation makes every assumption visible. Test rate and term changes, add the missing housing costs and compare the results with verified household evidence and written quotations.
Ask Crescent Capital to help organise your home-loan quotations for comparison. Crescent Capital cannot guarantee approval, a rate, a repayment or that one offer is best for every borrower.