🪙 Personal Finance Foundations

What you’ll learn

1. Now-You and Later-YouEstablish the course's through-line: every money decision moves value between present and future self at a price, and that price is an interest rate.Saving, borrowing, insurance and pensions aren't separate topics but one trade in different costumes — value moved between now-you and later-you at a price. The difficulty isn't arithmetic; it's that only now-you is in the room, and the discount applied to your future self (time preference) is universal and not a moral failing. What a course can usefully show you is the price of the trade, which is the part almost nobody reads.
2. Compounding Is the Exchange RateTeach compounding as the mechanism — interest earning interest — and give the rule of 72 as a portable tool.Simple interest always pays on the original principal and traces a straight line; compound interest pays on principal plus everything earned so far, and curves away. £1,000 at 7% for 30 years is £3,100 simple but £7,612 compounded — same deposit, same rate. The rule of 72 makes rates comparable instantly: 72 divided by the rate gives the doubling time.
3. The Same Curve, Pointed at YouShow that debt is the compounding formula with the sign flipped, using real Federal Reserve credit card rate data, and expose the interest/principal split.Compounding is indifferent to direction. Federal Reserve G.19 data shows average U.S. credit card rates rising from 14.60% in 2021 to 21.22% in 2025, with accounts assessed interest at 22.32% — a rate at which an unpaid balance doubles in about three years by the rule of 72. Minimum payments make almost no progress because roughly 1.8 points of a ~2% minimum is that month's interest, and the required payment shrinks as the balance does.
4. How a Rate Gets QuotedDistinguish APR from APY/AER, explain that the gap is compounding rather than a fee, and show how a flat fee converts to an annualised rate.APR is typically the periodic rate multiplied up; APY/AER accounts for compounding within the year, so 1.8% monthly is 21.6% APR but 23.9% effective. Products quote whichever convention flatters them — savings as APY, loans as APR — so rates must be converted to common units before comparison. A £15 fee on a two-week £100 loan annualises to roughly 390%, though whether that framing is fair to a short-term product is genuinely disputed.
5. A Budget Is an Instrument, Not a VerdictReframe a budget from a moral plan to a measurement instrument, and separate once-decided standing costs from repeatedly-decided daily ones.Luca Pacioli's 1494 textbook spread double-entry bookkeeping by making a business visible rather than merely felt — and a budget's job is the same: measurement, not judgement. Read as a plan it becomes a report card you stop consulting; read as an instrument it turns accidental spending into deliberate choice. Standing instructions like rent, insurance and subscriptions are usually larger than daily spending and change with a single decision.
6. The Emergency Fund Is Self-InsuranceReframe the emergency fund as self-insurance, connect its size to the deductible decision, and use Fed SHED data to show what it protects against.An emergency fund holds cash at a deliberately poor return against an unlikely event — the structure of insurance, with you as the pool, where the forgone return is the premium and certainty of access is the coverage. It follows that fund size and insurance deductible answer the same question: how much loss do I keep? The Fed's SHED survey shows the share of U.S. adults able to cover a $400 emergency with cash rising from 50% in 2013 to 68% in 2021 and settling at 63% through 2025 — a measure of circumstances, not character.
7. Inflation: the Silent Term of TradeTeach nominal vs real, use sourced BLS CPI data to show recent inflation, and explain inflation as a transfer from creditors to fixed-rate debtors.Real return is nominal return minus inflation, so a 1% account against 3% inflation loses about 2% of purchasing power while the balance rises. BLS CPI-U shows year-on-year June inflation of 1.6% in 2019, a 9.1% peak in 2022, and 3.5% by June 2026 — and a basket costing $100 in June 2017 costs $136.33 in June 2026. Inflation erodes fixed-rate debt in real terms too, transferring value from lenders to borrowers.
8. Liquidity, or Why the Shape of Money MattersIntroduce liquidity as a property of money's shape, and show that the extra yield on illiquid holdings is the price of surrendering optionality.The same £10,000 in a current account, a fixed bond, house equity or a friend's business behaves like four different substances, separated by how fast and at what discount each becomes spendable. Liquidity is optionality and optionality is valuable, so you're paid to give it up — which is why a fixed-term bond out-yields instant access. There is no free position: liquidity costs return, illiquidity costs flexibility.
9. Credit Scores Are a Machine, Not a JudgementExplain a credit score as a narrow prediction about a file rather than an assessment of a person, and show that its odd behaviours follow from that.A credit score answers one question — how likely is this file to miss payments on new credit — and is not a measure of wealth, income or virtue. Once seen that way, its strange behaviour is obvious: paying off a loan removes evidence, closing a card raises utilisation on the same balance, and no borrowing history means no prediction rather than a good one. Serious critiques exist about whether scoring encodes historical inequities; the mechanism is separate from that debate.
10. The Big Decision, and Why We Won't Answer ItShow the structure of the buy-versus-rent question, demonstrate why the common comparison measures nothing, and decline to answer it.Comparing rent to a mortgage payment errs in both directions at once: it counts principal — which buys an asset — as a cost, and omits maintenance, insurance, property taxes and lumpy transaction costs. The largest omitted term is usually the opportunity cost of the deposit. Because the arithmetic turns on personal facts like horizon, mobility and whether the difference would actually be invested, the answer is not universal and this course does not give one.
11. What You Now Know, and What You Don'tClose the through-line, consolidate the mechanisms learned, and state plainly the limits of what a course can advise about real money.Every chapter was the same trade — value between now-you and later-you at a price — so the portable question for any financial product is: what's the price, and which way is it pointing? Every figure in the course was either sourced and dated or labelled illustrative arithmetic, and none was a forecast. Understanding the machinery makes decisions legible, but what to do depends on a personal situation that requires a professional who knows it and is accountable for the advice.

Questions this course answers

Grounded in trusted sources

• Federal Reserve Statistical Release G.19, 'Consumer Credit' — Terms of Credit (https://www.federalreserve.gov/releases/g19/current/), retrieved July 2026
• Federal Reserve Board — 'Report on the Economic Well-Being of U.S. Households' (SHED), unexpected-expenses table (https://www.federalreserve.gov/consumerscommunities/sheddataviz/unexpectedexpenses-table.html), retrieved July 2026
• U.S. Bureau of Labor Statistics — CPI for All Urban Consumers, series CUUR0000SA0, via the BLS Public Data API, retrieved July 2026
• Luca Pacioli, 'Summa de arithmetica, geometria, proportioni et proportionalità' (Venice, 1494)
• Jane Gleeson-White, 'Double Entry: How the Merchants of Venice Created Modern Finance' (W. W. Norton, 2012)
• Irving Fisher, 'The Theory of Interest' (Macmillan, 1930)
• John Maynard Keynes, 'The General Theory of Employment, Interest and Money' (Macmillan, 1936)
• Adam Fergusson, 'When Money Dies: The Nightmare of the Weimar Hyper-Inflation' (William Kimber, 1975)

Every Wunder lesson is built from real, reputable sources — never invented.

Related Math courses