Guides

Plain-English explainers for the money ideas behind the calculators — what they mean, where they come from, and how to use them without being fooled by the maths. No sign-up, no jargon, no sales pitch.

The calculators give you a number; these guides give you the reasoning behind it. Each one is written in plain English by Tiaan Fourie and works through a single money idea — how loan amortisation actually splits interest from principal, why compound growth rewards time more than timing, what the 4% rule does and doesn't promise — without the jargon a textbook or a sales pitch would wrap around it.

Read a guide before you trust a result. Knowing why a calculator says what it says is what turns an estimate into a decision you can defend — and what stops a tidy on-screen figure from quietly misleading you.

How Loan Amortisation Actually Works — Your loan payment never changes, but the split between interest and principal shifts every month. Here is why early payments feel like treading water — and how to fix it. (7 min read)
Compound Interest: Why Time Beats Timing — Compound interest rewards patience more than cleverness. Here is how interest-on-interest works, why the last decade does the heavy lifting, and what quietly works against you. (6 min read)
The 4% Rule, and the Case Against It — The 4% rule is the most quoted number in retirement planning. Here is where it came from, what it actually promises, and why many planners now treat it with caution. (7 min read)
Five Budgeting Methods, Honestly Compared — There is no single best budget — only the one you will actually keep. Here are five popular methods, who each one suits, and where each one quietly falls apart. (6 min read)
How Much House Can You Really Afford? — The maximum a bank will lend you is a ceiling, not a target. Here are the costs a mortgage payment hides and a saner way to set your own limit. (7 min read)
Marginal vs Effective Tax Rates Explained — A raise into a higher tax bracket will not leave you worse off. Here is why brackets are marginal, what your effective rate really is, and when each number matters. (6 min read)
Buying a Car: How to Get the Numbers Right — How to set a car budget, choose new vs used, finance sensibly, and weigh the true cost of ownership — without being steered by the monthly payment. (8 min read)
Debt Snowball vs Avalanche: Which Pays Off Debt Faster? — The avalanche saves the most interest; the snowball keeps you motivated. Here is how each method works, when the gap actually matters, and how to choose. (7 min read)
How Big Should Your Emergency Fund Be? — Three months, six, or twelve? How to size an emergency fund on your real essentials, where to keep it, and why it comes before investing or extra debt payments. (6 min read)
Gross vs Net Pay: What Actually Lands in Your Account — Why your take-home is smaller than your salary, what the deductions are, and how to compare a salaried offer with an hourly rate on equal terms. (6 min read)