Finance calculators

Every finance calculator here follows the same rules: results update live as you type, the formula is shown with a worked example, and the math runs entirely in your browser — nothing you enter is uploaded anywhere. Each one is unit-tested against published reference values before it ships.

Which calculator answers which question

Money questions split into four shapes, and picking the wrong shape is why two calculators disagree. "What will this cost me each month?" is a repayment question — loan, bond, car and personal loan calculators all solve the same amortization formula, differing only in the defaults and the extras each purchase involves. "What can I afford?" runs that formula backwards from a monthly figure you can actually pay, which is the honest direction to work in before you shop. "What will this grow into?" is compound interest, where the compounding frequency and whether you add to it monthly matter more than the headline rate. And "how fast can I get out of this?" is the payoff family — extra payments, snowball, avalanche — which compares a debt against itself under different attack plans.

If you are early in a decision, start with affordability rather than repayment. A repayment calculator answers a question the bank has already framed for you; an affordability calculator makes you name your own ceiling first, which is the number that protects you when a salesperson starts extending the term to make a payment look small.

What every loan result here assumes

These calculators use the standard amortization formula for a fixed rate held for the whole term. Real credit agreements rarely behave that cleanly. An initiation fee is usually added to the amount borrowed, so you pay interest on it for the life of the loan. A monthly service fee sits outside the repayment figure and is easy to forget when comparing two quotes. Credit life insurance is frequently bundled in and is often quoted separately. On a variable rate — which most South African home loans are, being prime-linked — every rate change reshapes the schedule, and the payment you were quoted in month one is not the payment you make in year six.

The practical use of a repayment result is therefore not "this is what I will pay" but "this is the floor, and anything a lender quotes above it is fees I should ask about by name". The gap between our number and their number is the most useful thing on the quote.

Why the early payments are almost all interest

Interest is charged on what you still owe, and you owe the most at the start. On a twenty-year bond at a typical rate, the first payment can be more than three-quarters interest, and the crossover — the month where more of your payment goes to capital than to the bank — often does not arrive until somewhere past the halfway mark. This is not a trick; it falls directly out of charging interest on a declining balance. It does explain why paying a little extra early is so much more powerful than paying the same amount later: an early overpayment removes capital that would otherwise have accrued interest for the whole remaining term.

The amortization tables on the loan pages show this month by month, which is worth looking at once even if you never use it again. It reframes what an extra payment buys: not a slightly smaller balance, but the deletion of entire payments from the far end of the loan.

Compounding, inflation, and reading a growth number honestly

A compound-interest result is arithmetic, not a forecast. It tells you what a given rate produces if it holds for the entire period and you make every contribution on schedule — which no real investment does. Two adjustments make the number more useful. First, check the compounding frequency: monthly compounding on the same nominal rate beats annual, and a calculator that hides which it used is not worth trusting. Second, remember that the result is in future rands or dollars. Money that grows at 9% while prices rise at 5% has bought you roughly 4% a year in real terms, and over thirty years that distinction is the difference between comfort and disappointment. The inflation calculator exists precisely to translate a future figure back into money you can imagine spending.

A note on currency and VAT

The finance pages let you pick a currency because the mathematics is identical everywhere; only formatting and the sensible default rate change. VAT is the exception, because tax rates are jurisdictional: the VAT calculator handles both directions — adding tax to an exclusive price and extracting it from an inclusive one — and the second is where most errors happen. Removing 15% VAT from an inclusive price is not subtracting 15%; it is dividing by 1.15. On a R1,000 inclusive price the difference between doing it correctly and incorrectly is R19.57, which is small once and material across a year of invoices.