Invest · Lesson 3 of 3

The magic of compounding

Compound interest pays you on your money and on the interest you’ve already earned. Over decades, that’s the gap between “okay” and life-changing.

1Learn

  1. Time is #1Starting 10 years earlier can matter more than the exact dollar amount.
  2. Stay consistentSmall amounts added regularly beat one big lump sum you never start.
  3. Don’t break the chainWithdrawing early resets growth. Patience is the skill.

Quick math: the Rule of 72

Divide 72 by your yearly return to estimate how many years your money takes to double. At ~7% a year, 72 ÷ 7 ≈ 10 years.

It works both ways: compounding builds wealth for investors — and buries people who only pay credit card minimums. At 21% APR, debt doubles in about 3.4 years.

2Try it Calculator

Money working for you

Try 10 years, then 30.

After 30 years you’d have

$255,805

You put in$37,500

Growth$218,305

$1,500
$100
30 years
10%

Estimates for learning — not a promise of returns.

Rule of 72

Your money doubles in

~9.0 years

8%

3Check

Remember

When growth beats what you put in, your money is working harder than you are. Starting early and staying consistent beats “perfect” timing.

Go deeper: copy an investing prompt from Ask AI into your favorite AI tool — no private info needed.

Quick check

You invest at roughly 9% per year. About how long until your money doubles?