How Toolzeroo Finance calculates and checks its figures

Loan and bond repayments

Home loans, personal loans, car finance and most other South African credit are amortising loans: a fixed instalment pays the month's interest first and the rest reduces the balance. The calculators use the standard formula, with interest charged monthly at the annual rate ÷ 12:

Instalment = L × r ÷ (1 − (1 + r)^−n)

Here L is the amount borrowed, r the monthly rate and n the number of months. Example: a R 1 000 000 bond at 10.75% over 20 years (240 months) gives r = 0.10750 ÷ 12 and an instalment of about R 10 152 a month. Over the full term that is about R 1 436 549 of interest on top of the R 1 000 000 borrowed.

Monthly service fees are added to each instalment and once-off initiation fees to the total cost, because that is how they appear on a credit agreement. A car balloon (residual) is left unpaid until the last month, so the instalment repays only the rest. Affordability calculators run the same formula backwards: from the instalment you could afford to the loan it would support. The repayment percentage is your own assumption, so no lender's rule is hidden in the result.

Income tax, PAYE and the marginal method

Salary and tax calculators use the SARS individual tax tables for the tax year from 1 March to the end of February. Income is taxed band by band, the age rebates are taken off (primary, plus secondary from 65 and tertiary from 75), then medical scheme fees tax credits. Monthly PAYE on a regular salary is the annual tax ÷ 12. UIF is 1% of pay up to the monthly ceiling.

Example (2026/27): a salary of R 30 000 a month, age 30, is R 360 000 a year. Tax is R 44 118 + 26% of the R 114 900 above R 245 100 = R 73 992, less the R 17 820 primary rebate = R 56 172 a year, or R 4 681 a month. UIF is 1% of the R 17 712 ceiling = R 177,12. Take-home pay is about R 25 141,88.

When something is added to your income, such as a two-pot withdrawal, a taxable capital gain or a retirement deduction taken away, the calculators use the marginal method: tax on your income with the item, less tax on your income without it. A R 20 000 savings-pot withdrawal on top of a R 360 000 salary adds R 5 200 of tax, because all of it falls in the 26% band. SARS includes these amounts in your taxable income on assessment, so the extra tax is what the marginal method shows; the tax withheld on a fund’s tax directive can differ and is squared up on assessment.

Retirement fund lump sums and severance benefits are taxed on their own tables, which are cumulative: lump sums you received before use up the lower brackets first.

Savings, investment and inflation

Growth calculators compound at the rate you enter, monthly unless the calculator lets you choose, with contributions added at the end of each period:

FV = P × (1 + r)^n + C × ((1 + r)^n − 1) ÷ r

R 10 000 plus R 1 000 a month at 8% a year, compounded monthly for 10 years, grows to about R 205 142, of which R 130 000 is your own money. Returns are assumptions, not forecasts: real investments go up and down, and fees and tax reduce what you keep. Values in today's money divide by (1 + inflation) for each year. Tax-free savings stop contributions at the annual and lifetime limits, because SARS taxes anything above them at 40%.

Labour-law pay

The Basic Conditions of Employment Act (BCEA) sets the minimums for overtime, Sunday and public holiday pay, leave, notice and severance. For a monthly earner the Act's week is the monthly pay ÷ 4⅓, about 4.33 (section 35), and a day's pay is a week's pay ÷ the days worked in a week. The calculators show the legal minimum; your contract, a sectoral determination or a bargaining council agreement can give you more.

What the calculators do not do

• They do not know your full situation. A bank, employer, fund or SARS works from your complete records and its own rules, and can reach a different figure.
• They do not model everything on a payslip or tax return: fringe benefits, allowances, other deductions and once-off income can change PAYE.
• They assume the rate you enter stays the same for the whole period, unless the calculator says otherwise.
• Results are rounded to the cent for display; calculations use the unrounded figures.

The calculators are general education, not financial, tax or legal advice. For a decision that matters, confirm with the provider or the authority and speak to a registered professional.

How figures are checked and kept current

Official figures come only from the bodies that set them: SARS, National Treasury, the South African Reserve Bank, the National Credit Regulator, the Department of Employment and Labour, Stats SA, the Acts themselves and municipal publications. Before a new page or a changed figure goes live, a separate review checks every figure and rule against the official source, and the calculators are tested automatically against worked examples. Tax figures are reviewed after each February Budget, rate-linked notes after each SARB Monetary Policy Committee decision (next: 19 November 2026), labour figures when new amounts are gazetted and municipal rates each July. See the full review calendar.

Spotted an error or an outdated figure? Email privacy@toolzeroo.com with the page and the numbers you used.

Every calculator, its figures and sources

Generated from the same data as the How we calculate and sources box on each calculator, so the two always match.

Property and home loans

Loans

Salary and tax

Savings and investing

Credit and debt

Vehicles

Budget