How Pocket Rand works.

Start with your own quotes and estimates, change the inputs, and compare the results. Our examples are starting points, not live prices or offers. You can use the tools without an account, and calculations happen in your browser.

Three tools, three different questions

• Car ownership: compare two cars or payment options, including running costs and resale.
• Home-loan repayments: estimate repayments and the effect of extra payments. Assumptions are explained on the tool page.
• Solar payback: explore an estimated payback period using your installation cost, usable output and tariff. Assumptions are explained on the tool page.

Below is the detailed car-calculator methodology. If you prefer a practical walkthrough, start with our car-buying guides.

1. Monthly finance repayments

The amount financed is the purchase price minus the deposit. The balloon amount is a percentage of the original purchase price, and cannot be greater than the amount financed.

Let P be the amount financed, r the annual nominal interest rate divided by 12 (as a decimal), n the loan term in months and B the balloon amount.

Monthly instalment = (P − B / (1 + r)ⁿ) × r / (1 − (1 + r)⁻ⁿ)
At zero interest: monthly instalment = (P − B) / n.

Interest accrues on the opening balance each month. We deduct the instalment at the end of the month. At the final loan payment, the remaining balloon is paid separately. We keep full precision internally; displayed rands are rounded.

2. Selling before the loan ends

After each month: closing balance = opening balance × (1 + r) − instalment. If you sell early, this closing balance becomes the estimated settlement at sale. It includes the remaining balloon obligation; we do not add the balloon again.

For a sale at or after the end of the loan term, the balloon has already been paid and the balance is zero. We assume payments are made on time, with a sale immediately after a monthly payment. A lender’s actual settlement quote may include fees, accrued daily interest or other charges that this estimate excludes.

3. Fuel and running costs

Monthly fuel = kilometres per month ÷ 100 × L/100 km × rand per litre.
Monthly running costs = fuel + monthly insurance + (annual maintenance + annual tyres + annual licence) ÷ 12.

Annual expenses are budget provisions spread evenly over the period, rather than forecasts of the exact month you pay them. The same monthly distance and fuel price apply to both cars. For cars using different fuels, run separate comparisons or adjust the consumption input to test scenarios; the MVP models one fuel price at a time. It does not model EV electricity use.

4. Depreciation and resale

Estimated resale = purchase price × (1 − annual value-loss percentage)^(months owned ÷ 12).

This is a simple compounded assumption, not a valuation or market forecast. Tick “Use my own resale estimate” to override it. Depreciation then equals purchase price minus resale. Resale can exceed purchase price in a custom scenario, so a negative ownership cost is possible.

5. Cash flow and total ownership cost

For a financed car, cash paid out is the deposit + instalments paid + any balloon paid at maturity + running costs. For a cash purchase, it is purchase price + running costs.

Total ownership cost = cash paid out + remaining settlement − resale.
Equivalently: purchase price − resale + interest during ownership + running costs.

We divide total ownership cost by the ownership months to show average monthly ownership cost. That differs from regular monthly cash flow (instalment + running costs). Neither the deposit nor balloon is hidden inside the regular monthly cash-flow figure. The tables show both separately. Cost per kilometre is total ownership cost divided by total distance; at zero kilometres, it is not applicable.

A worked example you can check

Suppose a car costs R120,000. You put down R20,000, borrow R100,000 at 0% for 60 months, and owe a R20,000 balloon. Your regular payment is R1,333.33. After 24 payments, the outstanding balance is R68,000.

If you sell for R80,000 after 24 months with R2,000 monthly running costs: cash paid is R20,000 + R32,000 + R48,000 = R100,000. Add R68,000 settlement and subtract R80,000 resale: total ownership cost is R88,000, or R3,666.67 per month. The equivalent check is R40,000 depreciation + R0 interest + R48,000 running costs.

What is outside this model?

Loan initiation and monthly service fees, optional extras, trade-in arrangements, insurance excesses, unexpected repairs beyond your budget, parking, tolls, taxes, inflation, changing interest rates, business deductions and the opportunity cost of using cash. Include a separate allowance for these. A cash-versus-finance comparison is incomplete without considering your own cash needs and the return you could otherwise earn.

Methodology version 1 · reviewed 18 October 2026. General planning information, not a quote or personal financial advice.