TRANSPARENT METHODS · LAST REVIEWED NOVEMBER 2026

How our decision tools work

Is This or That? provides rough decision models, not prices scraped from stores or personalised financial advice. We publish the underlying assumptions because a useful calculator should be explainable and easy to challenge.

1. Grocery promotions

Unit price = price ÷ package size (using consistent units). Effective price per used unit = price ÷ (package size × usable fraction). Compare options only when their usable quality and quantity are comparable. Example: R75 for 1 kg, with 70% actually used, equals R107.14 per kg consumed. A bulk pack can be cheaper per unit purchased but more expensive per unit used.

2. Total ownership cost

Estimated ownership cost = purchase price + recurring running costs + expected maintenance and replacement expenses − any realistic resale value. Use one consistent time horizon. Example: R8,500 upfront plus R1,100 per year for five years totals R14,000 before maintenance and resale. This simplified model does not automatically discount future cash flows or predict future energy prices.

3. Comparing purchase options

Scores depend on the preferences and weights entered by the visitor. They are not independent product test results. Evaluate mandatory constraints first, then compare trade-offs. Re-run the comparison with changed weights; if small changes reverse the winner, treat the result as a close call.

4. Collect versus courier

Collection cost = return-trip distance × (fuel consumption per distance × fuel price + estimated wear per distance) + parking/tolls + estimated time cost. Compare that with the delivery price. For an already-planned trip, use the extra distance and time, not the entire trip. Example: 30 km × (7.5/100 × R24 + R0.80) + R45 = R123.

How we validate the models

• Check units and currency before comparing amounts.
• Test zero-cost, equal-cost and boundary cases.
• Recalculate worked examples independently.
• Check how sensitive results are to uncertain inputs.
• Correct reported errors and update explanations when assumptions change.

Known limitations

Results are estimates based on visitor inputs, not guarantees. The site does not independently verify retailers, prices, energy ratings, vehicle consumption, product quality, delivery reliability or potential resale values. Do not treat a small estimated difference as a precise saving. Currency selection changes formatting and denomination, not necessarily live exchange rates.

Corrections and transparency

Have you spotted an incorrect formula or example? Please include the tool URL, input assumptions and expected result in a message to [email protected]. The service is operated by VA TECH (PTY) LTD, Johannesburg, South Africa, registration 2017/520605/07.

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