1 Chapter 1 of 9 · 9 min read · Updated September 22, 2026
Money Basics
Four ideas decide everything else in investing: inflation, compounding, risk, and time. This chapter covers all four in about ten minutes.
Core facts
- Cash loses buying power every year. At 3% inflation, prices double about every 24 years, so a dollar kept in a drawer buys half as much by then.
- Investing means accepting uncertainty in exchange for expected growth. Higher expected returns always come with higher risk. There is no exception.
- Compound growth is returns earning returns. Divide 72 by the yearly growth rate to get the doubling time: 7% doubles money in about 10 years.
- The U.S. stock market has averaged roughly 7% a year after inflation over long periods. Single years range from about −40% to +40%.
- Your time horizon, when you need the money, decides how much risk you can take. Money needed within 2 years stays in cash. Money not needed for 20 years can be fully invested.
- Before investing: keep 3 to 6 months of expenses in cash, and pay off any debt charging more than about 8% a year. Paying off 20% credit-card debt is a guaranteed 20% return.
What money does
Money does three jobs. Investing is only about the third one.
- Medium of exchange: you trade work for money and money for things, instead of trading work for things directly.
- Unit of account: prices are written in it. "A loaf costs $3" is a measurement.
- Store of value: it carries this month's earnings into the future. This is the job money does worst, because of inflation.
Inflation
Inflation is the general rise in prices over time. When prices rise, each dollar buys less. Nothing happens to the dollar itself; the world around it gets more expensive.
In the U.S. it is measured by the Consumer Price Index (CPI), which tracks the cost of a fixed basket of everyday items: food, rent, fuel, services. "Inflation was 3% this year" means that basket costs 3% more than a year ago.
Small percentages compound. The table shows what $100 in cash still buys after sitting untouched at 3% inflation.
| Years | Buying power of $100 |
|---|---|
| 5 | $86 |
| 10 | $74 |
| 20 | $55 |
| 40 | $31 |
Two consequences:
- "Just save it" is not a plan for money you will hold for decades. Cash is safe from sudden loss and exposed to slow loss.
- A return only counts after inflation. Earning 3% while prices rise 3% is a real return of zero. The number before inflation is the nominal return.
Low, steady inflation (around 2%) is the target of most central banks and is normal. It only becomes a problem when you ignore it.
Compound growth
Compound growth is growth on top of growth. If an investment earns 7% and you keep the earnings invested, next year's 7% is calculated on a larger amount. The gains produce their own gains.
The Rule of 72 gives the doubling time: divide 72 by the yearly rate.
| Yearly growth | Doubles every | $10,000 after 40 years |
|---|---|---|
| 3% | 24 years | about $33,000 |
| 5% | 14 years | about $70,000 |
| 7% | 10 years | about $150,000 |
| 10% | 7 years | about $450,000 |
Three things follow:
- Small differences in yearly rate become huge differences over decades. This is why fees matter (Chapter 3).
- Most of the growth arrives late. The last ten years of a forty-year run produce more than the first thirty combined.
- Time is worth more than money. $100 a month started at 25 usually beats $200 a month started at 40.
Risk
Risk is uncertainty about what you get back. Cash in an insured bank account is nearly certain. A single company's stock is not: in ten years it could be worth three times as much, or nothing.
The rule that governs all of investing: higher expected returns come with higher uncertainty, and nobody can honestly separate them. Any offer of high returns with no risk is a mistake or a scam.
Four kinds of risk you will meet in every chapter:
| Kind | What it is | What reduces it |
|---|---|---|
| Market risk | Everything falls at once (2008, March 2020). | Time. Spreading out does not help. |
| Specific risk | One company, coin, or bond fails. | Diversification: owning many, not one. |
| Inflation risk | Cash quietly loses buying power. | Owning assets that grow. |
| Behaviour risk | You sell in a panic or buy in a frenzy. | A written plan and automatic investing. |
Volatility, the daily up-and-down of prices, is not the same as loss. The real danger is permanent loss: money you needed, gone for good. Money you will not touch for twenty years can tolerate a lot of volatility. Money you need next year cannot.
Time horizon
Your time horizon is how long the money can stay invested before you must spend it. It is the single most important input to every later decision.
| Need the money in | Can it be in stocks? | Where it usually goes |
|---|---|---|
| Under 2 years | No | Savings account, money market fund, short-term Treasuries |
| 2 to 5 years | Partly | Mostly bonds and cash, some stocks |
| 5 to 10 years | Mostly | A mix leaning toward stocks |
| 10+ years | Yes | Mostly or entirely stock index funds |
Why: the U.S. stock market has had many terrible years and several terrible five-year stretches. It has had no losing 20-year stretch in recorded history. That is a description of the past, not a guarantee, but it is why long horizons can ignore short-term drops.
Before you invest
Three steps come before the first dollar goes into the market. They are boring and they work.
1. Keep an emergency fund
An emergency fund is cash for a lost job or a broken car. Target 3 to 6 months of essential expenses. Keep it in a savings account, not the market, because the day you need it is often the day the market is down. One month is a real start.
2. Pay off expensive debt
Credit cards charge around 20% a year or more. No investment reliably beats that. Paying the debt off is a guaranteed return equal to the interest rate, which is the best deal a beginner will ever get. Cheap debt, like a low-rate mortgage, is a separate decision. See credit cards and credit scores.
3. Separate saving from investing
- Saving is money kept safe for known, near-term needs.
- Investing is money exposed to risk in exchange for growth, for needs that are years away.
Investing next month's rent, or "saving" for retirement in a cash account, are the two most common beginner errors. Both come from mixing these up.
Write down three numbers: your monthly essential expenses, the balance on any debt above 8% interest, and the number of years until you will need the money you plan to invest. Those three numbers are your starting position for the rest of the course.
Common mistakes
- Holding long-term savings in cash for years because it feels safe. It is safe from crashes and guaranteed to shrink.
- Investing money needed within two years, then being forced to sell during a drop.
- Investing while carrying 20% credit-card debt. The debt outruns any realistic return.
- Treating a good year as normal. The long-run average is about 7% after inflation; almost no single year is average.
- Believing an offer of high returns with low risk. It does not exist.
Remember
- Inflation shrinks cash. Compounding grows investments. Both are slow, then dramatic.
- Return and risk are sold as a pair.
- Time horizon decides how much risk is appropriate. Short money stays in cash; long money can be invested.
- Emergency fund first, expensive debt second, investing third.
Common questions
Is keeping cash ever right?
Yes. For money you need within about two years, for your emergency fund, and for any amount that lets you sleep. Cash is the wrong place only for money you will not touch for many years.
Where does the 7% number come from?
It is the approximate long-run average yearly return of the broad U.S. stock market after inflation, measured over roughly a century. Individual years vary from about −40% to +40%. Use it for planning, not prediction.
Is a high-yield savings account investing?
No. It is saving that roughly keeps pace with inflation. It is the right home for an emergency fund and for money needed within a couple of years.
How much money do I need to start?
Very little. Most brokers sell fractional shares, so $5 to $50 is enough to begin. The amount matters less than whether the money is truly not needed for years.
Pay off debt or invest first?
Debt charging more than about 7 to 8% a year is usually worth clearing first, because paying it off is a guaranteed return of that rate. Very cheap debt is a judgement call. This is a general principle, not advice.