Einstein probably never called compound interest “the eighth wonder of the world” — but the quote survives because it feels true. Let's see why, with a curve you can bend yourself.
Growth on growth
Put $1,000 somewhere that grows 10% a year. Year one you gain $100. Year two you gain $110 — because the $100 you earned is now earning too. Year three, $121. The base keeps getting bigger, so the growth keeps getting bigger.
Play with the curve
Watch the green area (growth) overtake the blue area (what you put in). Then tick “start 10 years later”.
The most important number isn't the amount. It's the number of years.
The rule of 72
Divide 72 by the yearly rate to get the doubling time: at 6% → ~12 years, at 9% → ~8 years. It works because of logarithms, but you don't need them — just remember 72 ÷ rate.
Quick check
At 8% per year, roughly how long does money take to double?
The dark side: debt compounds too
Credit cards at 20%+ per year use the same maths against you: an unpaid balance doubles in about 3.6 years. Paying off high-interest debt is often the best “investment” there is.
Compounding beyond money
- Skills: each thing you learn makes the next one easier.
- Content & SEO: every article keeps bringing visitors for years, and they add up.
- Audience: followers bring followers — see how things go viral.