How We Calculate

Methodology, formulas and sources · Last verified 11 June 2026

Every figure on Finance Atlas comes from a published formula and a verifiable source — not a black box. This page sets out exactly how the calculators work, which fee caps and tax tables we apply, where those numbers come from, and how we test the maths. If you ever get a result that looks wrong, this page is how you check our working.

The core formula: amortisation

The vehicle finance, home loan and personal loan calculators all use the standard amortisation formula that South African banks use. For a loan of principal P at a monthly interest rate i (annual rate ÷ 12) over n months, the monthly payment is:

PMT = P × i ÷ ( 1 − (1 + i)⁻ⁿ )

Where a balloon (residual) applies, the portion of the loan represented by the balloon is not amortised — it is discounted back to today and subtracted before the payment is worked out, then falls due as a lump sum at the end of the term:

PMT = ( P − FV ÷ (1 + i)ⁿ ) × i ÷ ( 1 − (1 + i)⁻ⁿ )

National Credit Act fees

The National Credit Act (NCA) caps the fees a credit provider may charge. We apply the maximum permitted figures, since that reflects most real-world quotes, and we include them where many online calculators leave them out:

Initiation fee (vehicle & personal loans): R1,207.50 incl. VAT, once-off, assumed capitalised into the loan.
Initiation fee (home loans): R6,037.50 incl. VAT, once-off, assumed capitalised into the bond.
Monthly service fee: R69.00 incl. VAT, added to every instalment for the full term.
Credit life insurance (unsecured credit): capped at R4.50 per R1,000 of the outstanding balance per month, so it declines as you repay.

Source: National Credit Act, 2005 and its regulations, administered by the National Credit Regulator (NCR). Caps are reviewed by the regulator over time; we update them when they change.

Interest rates

Default rates are quoted relative to the prime lending rate, which sits at a fixed 3.5 percentage points above the South African Reserve Bank (SARB) repo rate. As at our last verification, the repo rate is 7.00% and prime is 10.50%. The SARB's Monetary Policy Committee reviews the repo rate up to six times a year; when it moves, we update our central rate file and the "rates last verified" stamp shown on every calculator.

Source: South African Reserve Bank (SARB) Monetary Policy Committee statements. Your own rate depends on your credit profile and is set by your bank as prime plus or minus a margin.

Transfer duty

The transfer costs calculator applies the official SARS transfer duty table for the 2026/27 tax year — a sliding scale where no duty is payable below R1,210,000 and rising marginal rates apply to the value within each bracket. Attorney, Deeds Office and sundry figures are clearly-labelled guideline estimates, not fixed charges, because they vary between firms.

Source: South African Revenue Service (SARS) transfer duty tables, effective 1 April 2026.

How we verify accuracy

Every calculator engine is tested before it ships. Amortisation results are checked by independently simulating the loan month-by-month and confirming the outstanding balance closes to zero (or to the balloon) at the end of the term. The settlement calculator's outstanding-balance formula is cross-checked against a month-by-month simulation and matches to the cent. The transfer duty engine is validated against published worked examples across every bracket. We re-run these checks whenever a formula or rate changes.

What these calculators are not

They are educational estimates. They cannot see your credit profile, the specific vehicle or property, lender-specific pricing, or add-ons bundled into a deal — all of which move the real number. Finance Atlas is not a registered Financial Services Provider (FSP) under the FAIS Act, and not a registered credit provider under the NCA. Always confirm the exact figures with your bank or a registered FSP before signing anything. See our full Terms of Use.

Spotted something wrong?

If a result looks off, tell us the exact inputs and what you expected via the contact page. Accuracy is the whole point of this site, and corrections from people who know their own numbers are genuinely useful.