Methodology

Tax calculators

Every rate, bracket, threshold, rebate, and cap in every tax calculator comes from a primary source — typically SARS or National Treasury:

• Income tax, PAYE, rebates, medical credits, provisional tax, retirement deductions, capital gains, SBC, turnover tax, transfer duty, donations tax, wear-and-tear, VAT — SARS rate tables and the annual Budget Speech.
• UIF benefits — Department of Employment and Labour UIF Amendment schedules.
• Municipal rates — per-municipality rates policies published under the Municipal Property Rates Act.

Where a calculator page shows a rate table, the bracket values match the corresponding SARS page. We link the specific source on each calculator under “Source.”

Medical aid tools

Medical aid contribution data is sourced directly from each scheme’s published member guides and benefit tables — the same documents you receive as a member or can download from the scheme’s website. Specifically:

• Monthly contributions — taken from each scheme’s current member guide or rate schedule, typically effective 1 January as published by each scheme.
• Benefits and limits — day-to-day benefits, hospital cover, savings account allocations, and annual limits as stated in the scheme’s benefit option summary.
• Scheme registration — all schemes shown are registered with the Council for Medical Schemes (CMS). Registration numbers are available on the CMS website.

Contributions and benefits change annually. We update the medical aid data at the start of each calendar year when schemes publish new rates. If you notice a discrepancy between what we show and your scheme’s current member guide, please flag it — see “Submit a correction” below.

The medical aid comparison tool is a planning aid only. Scheme eligibility, waiting periods, late-joiner penalties, and underwriting conditions are not modelled. Always confirm terms with the scheme or a registered broker before switching.

Savings, debt, and property tools

These calculators use standard financial mathematics — no proprietary models:

• Home loan and vehicle finance — standard amortisation formula (equal monthly instalments) with National Credit Regulator guidance on permitted initiation and service fees (NCA Schedule 1).
• Savings and compound growth — periodic compound interest formula. TFSA contribution limits follow National Treasury’s published annual caps.
• Retirement annuity projections — compound growth with SARS-published deductibility limits and lump-sum tax tables.
• Prime interest rate — the South African Reserve Bank (SARB) repo rate plus the standard 3.5% margin. We update this manually after each Monetary Policy Committee (MPC) announcement.

Projections assume a constant rate over the full term. Real-world rates change — use projections as directional estimates, not guarantees.

How a calculator is built

Three layers separate concerns cleanly across all tools:

1. Config. Source data (SARS brackets, scheme contribution tables, NCA fee caps) lives in versioned TypeScript config files. Updating a rate is a one-line edit — the calculation engine and UI are untouched.
2. Engine. Pure functions that take a config and your inputs and return a result. No side effects, no network calls — calculations are deterministic and validated through automated tests.
3. UI. A React form that collects your inputs, runs the engine in your browser, and displays the result. Your inputs never leave the page.

Tax-year versioning

South African tax years run from 1 March to the following 28/29 February. When the Budget Speech introduces changes, we add a new config file for the upcoming year and keep prior years available. Calculators default to the current year but let you select a prior year — useful when filing late or reviewing a historical return.

Older blog posts may reference rates from the year they were written. We flag those with a “Tax year” marker and update related calculator pages when a rate changes materially.

What the tools don’t do

All results are estimates that assume standard cases. They don’t model:

• Double-tax-treaty relief for foreign income.
• Farming, mining, or trust special rules.
• VAT apportionment or complex input-tax claims.
• Your specific SARS assessment history, penalties, or interest accrued.
• Medical aid waiting periods, late-joiner penalties, or scheme-specific underwriting conditions.
• Variable interest rate scenarios for home loan or savings projections.

Update cadence

• Annually (March), after the February Budget Speech — new tax-year config, review of all SARS-dependent calculators.
• Annually (January), when schemes publish new rates — medical aid contribution and benefit data refreshed.
• After each MPC meeting — prime rate updated if the repo rate changes.
• On correction — if a reader flags a verified bug we fix it as soon as possible.

Not financial advice

Nothing on Mzansify is professional tax, financial, or legal advice — see the disclaimer for full terms. Use the tools to understand likely numbers, then consult a registered tax practitioner, financial advisor, or medical aid broker for anything you’ll act on.