Every formula used in this calculator is based on established financial mathematics and official South African tax legislation. The sources below allow you to independently verify each calculation.
Where P = initial capital, r = annual rate (decimal), n = months, PMT = monthly contribution. When r = 0, the formula simplifies to FV = P + PMT × n (no division by zero).
Algebraic rearrangements of the FV formula. The annual rate solver has no closed-form solution and uses bisection search (120 iterations, converges to 10⁻¹⁰ precision) — a standard numerical method for root finding.
Converts a future nominal rand amount into today's purchasing power by deflating at the assumed inflation rate. South Africa's long-run CPI average is approximately 5–6% per annum (SARB data).
SARS taxes only a portion of your capital gain (the "inclusion amount"). For individuals the inclusion rate is 40%. At the top marginal rate of 45% this gives a maximum effective CGT rate of 18%. A R40,000 annual exclusion also applies per person (not modelled here as it requires an annual realisation schedule).
A flat 20% tax withheld at source on dividends paid by SA-resident companies to individual shareholders (effective 22 February 2017). Governed by Section 64E of the Income Tax Act No. 58 of 1962.
Standard present-value annuity formula in reverse — models a capital balance that earns compound interest while making regular withdrawals. Depletion occurs when expenditure exceeds monthly income from capital.