The piece about the maths and the mental models underneath every money decision you will ever make.
You have picked up the Foundations piece of the jigsaw. What follows is the shelf underneath it — everything on the site that helps you build the maths and the mental models: the related questions from the ten, the chapters from the book, the courses, the eBooks, the blog posts and the newsletter issues. Browse the whole lot or jump straight to the bit you need.
What Foundations covers
Many money mistakes and problems happen because of simple misunderstandings of basic concepts. Someone takes out a payday loan because the APR looks like a small number next to the borrowing amount. Someone keeps £8,000 sitting in a current account earning nothing because the word “investing” sounds like gambling. Someone panic-sells in a crash because the loss feels twice as bad as the gain felt. Every one of those is a foundations problem, and every one of them is fixable once you know what to look for.
This shelf covers the maths first: percentages (properly — including the ones that quietly ruin people), simple and compound interest, the Rule of 72, the time value of money, probability versus odds (a distinction the betting industry relies on you not making), and the real-versus-nominal trick inflation plays. Then the mental models: risk as something you tolerate rather than avoid, opportunity cost as the question behind every choice, net worth as the one number that matters more than income, and the cognitive biases that keep otherwise smart people doing daft things with money. It also covers how banks actually work as businesses (so you stop being surprised by their behaviour), foreign currency and exchange rates, and enough spreadsheet literacy to plan a month without reaching for an app.
How to use this shelf
If you read nothing else on this site, read the compound interest question below. Not because it is the most urgent — it is not — but because it is the single idea that makes everything else on every other shelf make sense. Once you understand compound interest properly, the saving shelf stops looking boring, the investing shelf stops looking terrifying, and the borrowing shelf starts looking like the trap it actually is. If you are here because a specific decision is in front of you today (a loan, a credit card, a savings product), skip to the question page closest to that decision and come back to the rest of this shelf afterwards. And if you are here because someone has made you feel stupid about money, read “Am I being ripped off?” first — the cognitive bias chapter in the book is the best answer to that feeling, and this is the shelf it lives on.
What is on the Foundations shelf
Questions from the Ten
I do not know where to start with money — the entry-level question. Foundations sits underneath it because before you pick a bank or a budget app, a handful of maths and mindset ideas make the rest of the decisions obvious. Read →
How do I know I am not being ripped off? — the shelf’s most-used question. The cognitive bias chapter in the book is why so many people feel permanently behind on money — and why the answer is almost never “try harder”. Read →
What is the deal with ISAs? — the maths of tax wrappers, the rule of 72 applied to Cash versus Stocks and Shares, and the Foundations-side explanation of why the £20,000 allowance is less generous than it sounds once you account for inflation. Read →
Is crypto worth it? — the risk, probability and expected value question. Foundations is why the honest answer is “it depends on what you mean by investment” rather than yes or no. Read →
How do I get rich? — the compound interest question, dressed up. The only reliable answer to “how do I get rich” is a Foundations answer: time, rate, and not interrupting the compounding. Read →
Courses
Coming soon — Module 1 of the Money Sorted financial literacy courses covers the Foundations piece end to end: percentages, interest, time value of money, probability, risk, cognitive bias, opportunity cost, and spreadsheets for planning. Sign up to the newsletter below to hear when it goes live.
eBooks
Time Superpower — the compounding cheat code (free, coming soon). The short, free eBook on why time, not money, is the most valuable thing a 17-year-old has on their side. This is the Foundations shelf’s lead eBook — it takes the compound interest idea and turns it into a single actionable story. The book every Money Sorted reader should start with.
The Money Traps eBook (paid, coming soon). Covers the Foundations-side traps: APR versus AER, the representative rate that is not the rate you will actually get, and the behavioural tricks product designers rely on.
Blog posts
No live blog posts on Foundations yet. The first post on this shelf will be a walkthrough of the Rule of 72 — how to use it in your head in ten seconds to sanity-check any savings, loan or investment number anyone ever quotes you. Published weekly — see the full Blog.
Newsletter
Sign up to the weekly Money Sorted newsletter for short, practical pieces on the maths and the mindset alongside everything else on the site. Subscribe →
Podcast
The Money Sorted podcast is in production. When it launches, episodes tagged “Foundations” will appear here automatically.
Related pieces of the jigsaw
The Foundations shelf underpins every other shelf on the site — it is the one you keep coming back to. These three lean on it the hardest.
Heard enough, want to get started? The fastest route into the Foundations shelf is the compound interest question — everything else on every shelf falls into place once you understand it.
Not sure Foundations is the right shelf? Put this piece down and pick another from the jigsaw, or try the ten questions for a guided route.