Investing, Risk, and Return
Compare saving, stocks, bonds, mutual funds, diversification, risk, return, time horizon, and compound interest.
A lesson of Economics, in Personal Finance, about 10 minutes.
Investing: Risk, Return, and the Power of Time
By the end of this lesson, you will be able to explain the risk-return trade-off, describe major investment vehicles, apply compound interest, and explain why time is the most powerful investing tool.
The Risk-Return Trade-Off
Risk: the possibility that your investment will lose value (or not grow as expected).
Return: the gain from an investment (income + price appreciation), expressed as a percentage per year.
Fundamental rule: higher expected return always comes with higher risk. There is no free lunch.
| Investment | Risk | Average annual return |
|---|---|---|
| Savings account | Very low | 0.5–5% (varies) |
| US Treasury bonds | Very low | 4–5% currently |
| Corporate bonds | Low-moderate | 5–7% |
| Large-cap stocks | Moderate-high | ~10% historically |
| Small-cap stocks | High | ~12% historically |
| Cryptocurrency | Very high | Highly variable |
Compound Interest
$$A = P\left(1 + \frac{r}{n}\right)^{nt}$$
Simple version for annual compounding: $A = P(1+r)^t$
Example: $10,000 invested at 7% annual return for 30 years:
$A = 10000 \times (1.07)^{30} = 10000 \times 7.612 = $76,122$
The $10,000 grew to $76,122 — $66,122 was from compound growth.
Rule of 72: years to double = 72 ÷ interest rate
At 8%: doubles in 9 years. At 4%: doubles in 18 years.
The Time Advantage
Start early: the most powerful investment decision you can make.
| Investor | Starts | Stops | Annual investment | Amount at 65 |
|---|---|---|---|---|
| Early Emily | Age 22 | Age 30 (8 years) | $5,000 | ~$600,000 |
| Late Larry | Age 30 | Age 65 (35 years) | $5,000 | ~$550,000 |
Emily invested for only 8 years; Larry invested for 35. Emily comes out ahead because she started earlier — time is more valuable than contribution amount.