Mortgage Repayment Calculator South Africa
Estimate principal-and-interest home loan repayments, then see how an extra amount could change total interest and the payoff date. Weekly, fortnightly and monthly frequencies use their own payment periods instead of simply halving a monthly figure.
Set the home loan assumptions
Calculate to compare the contractual schedule with your extra-repayment plan.
Rate pressure check
The repayment begins with the balance, rate, term and frequency
A mortgage repayment estimate is based on the amount borrowed, not the advertised property value. If a R650,000 home is bought with a R130,000 deposit and no other amount is added to the loan, the starting principal is R520,000. Lenders mortgage insurance, capitalised fees or a refinanced balance can increase that principal. Enter the number that will actually accrue interest.
Principal-and-interest formula
The calculator uses the standard amortising payment formula: payment equals principal multiplied by r(1+r)n, divided by (1+r)n minus 1. Here r is the annual rate divided by the selected number of repayments per year, and n is the total number of repayments. At a genuine 0% rate, the tool divides principal evenly by n. Intermediate balances keep full precision; only displayed money is rounded to cents.
The formula assumes one unchanged rate for the whole term and interest compounded on the same frequency as the repayment. Actual South African variable home loan rates can change, and many lenders calculate interest daily before charging it monthly. The result is therefore a consistent scenario for comparing terms and extra payments, not a reconstruction of a lender’s day-by-day ledger.
Frequency is calculated directly
Fortnightly mode uses 26 periods per year and weekly mode uses 52. It does not take a monthly repayment, divide it by two or four, then call that the minimum. Paying half the monthly amount every fortnight creates 26 half-payments, equivalent to 13 monthly payments, and can act like an extra annual payment. That can be a useful strategy, but it is different from asking for the mathematically equivalent required fortnightly repayment. Use the contract’s required payment when checking affordability.
Early repayments contain more interest because the balance is larger
Each payment first covers interest for the period and the remainder reduces principal. At the start of a long loan, the balance is close to the original amount, so the interest portion is comparatively large. As principal falls, less interest accrues and more of the unchanged payment reaches principal. This is amortisation; it explains why the balance does not fall by the full payment amount and why an extra dollar paid early can influence many later periods.
Worked monthly example at 6.15%
For a R500,000 principal-and-interest loan over 30 years at 6.15% with monthly compounding, the scheduled repayment is approximately R3,046.14. If the rate never changes and there are no fees, 360 payments total about R1,096,610.69, of which roughly R596,610.69 is interest. The interest is larger than the original principal because a substantial balance remains outstanding over three decades.
Adding R200 to every monthly repayment raises the cash payment to about R3,246.14. Under the same model, the balance clears in roughly 305 months, around 25 years and 5 months. Interest falls to approximately R489,221.32, saving about R107,389.36 and 55 monthly payments. The final payment will usually be smaller than the regular amount because it only needs to clear the remaining balance and that period’s interest.
A rate stress test turns affordability into a range
The entered rate describes one scenario. The result panel recalculates the scheduled repayment at two and three percentage points above it while keeping the principal, remaining term and frequency unchanged. For the R500,000, 30-year monthly example, 8.15% produces a repayment near R3,721.24 and 9.15% produces about R4,077.19. The three-point scenario is more than R1,000 a month above the 6.15% payment.
A stress result is not a forecast that rates will move by exactly that amount. It is a cash-flow question: could the household absorb the higher figure after council rates, strata, insurance, maintenance, utilities, childcare and other debt payments? If the answer depends on stopping all savings or using a credit card for irregular bills, the comfortable loan amount may be lower than the maximum a lender is willing to approve.
| Change | Regular repayment | Total interest | Practical trade-off |
|---|---|---|---|
| Larger deposit | Usually lower | Lower | Uses more cash before settlement |
| Shorter term | Higher | Lower | Less monthly flexibility |
| Lower rate | Lower | Lower | May involve fees, conditions or refinancing cost |
| Regular extra repayment | Higher by choice | Lower | Needs redraw or cash-buffer planning |
Match the model to the product before acting on the result
This calculator is for principal-and-interest loans with regular payments. It does not model an interest-only introductory period, construction drawdowns, bridging finance, a split fixed/variable structure, offset-account balances that change daily, redraw transactions, package fees or a line of credit. Those features change either the balance path or the cash flow and deserve their own scenario rather than a hidden adjustment.
The interest rate is not the comparison rate. A comparison rate combines the advertised rate with most fees using a standardised example, which can help screen products. To model a specific contract, enter the actual interest rate and separately account for establishment, annual package, valuation, settlement, discharge and switching costs. A lower rate can take time to recover refinancing expenses, especially when the remaining balance or term is small.
Extra repayments are simulated from the first selected period and remain constant. If the plan is a one-off lump sum, reduce the principal at the date it will be paid or use a dedicated lump-sum schedule. If extra payments start in three years, the early balance will have followed the base path until then, so applying the extra from day one overstates the saving. The timing of money matters as much as its nominal amount.
Keep purchase cash and mortgage principal in separate plans
The loan amount is only one part of the cash required to buy and hold a property. Stamp duty, conveyancing, inspections, moving expenses and an initial repair buffer may be paid outside the mortgage, while lenders mortgage insurance can sometimes be added to it. Do not increase the deposit in this model without also checking that enough accessible cash remains for settlement and early ownership costs. Conversely, do not enter the full property price when a deposit has already reduced the amount borrowed. A clean separation between purchase cash, financed principal and ongoing housing costs makes the repayment useful in a household budget and prevents the same cost being counted twice.
Use the output to compare clearly stated scenarios, then request a lender repayment schedule for the actual product. A calculator cannot decide eligibility, borrowing capacity or whether a property purchase is suitable. It can, however, reveal when a longer term lowers today’s payment by shifting much more interest into later years.
Home loan repayment questions
Why is the calculated fortnightly repayment not exactly half the monthly repayment?
The calculator derives each frequency from its own periodic rate and number of periods. Half a monthly amount paid 26 times creates the equivalent of 13 monthly payments, which is an extra-payment strategy rather than the mathematically equivalent minimum fortnightly schedule.
Will a lender that calculates interest daily give the same cents?
Not necessarily. Daily balance changes, payment dates, leap years, rate changes and lender rounding can create differences. This model follows the stated assumption of compounding on the selected repayment frequency, which is useful for consistent comparisons but not a payout quote.
Should money in an offset account be subtracted from the loan amount?
For a simple snapshot, subtracting a stable offset balance can approximate the amount on which interest is charged, but it will not reproduce cash movements or fees. If the offset rises and falls with salary and expenses, use a cash-flow model rather than treating it as a permanent principal reduction.
What if I plan one large extra payment instead of a regular amount?
The regular-extra field assumes the amount is paid every period from the beginning. A lump sum paid later saves less than the same amount paid now because interest accrues before it arrives. Model the balance at the intended date, reduce it by the lump sum, then calculate the remaining term.
Why are annual package fees missing from total interest?
Fees are cash costs, not interest generated by the amortisation formula. They vary by product and can persist even when the balance falls. Add them separately when comparing loans so a discounted rate is not evaluated without the package price required to obtain it.