Why Compound Interest Is the 8th Wonder of the World
Albert Einstein reportedly called compound interest "the eighth wonder of the world." Whether he actually said it or not, the math doesn't lie: compounding transforms modest savings into life-changing wealth over time.
The Start Early vs. Start Late Dilemma
Meet two investors:
- Alex starts investing $500/month at age 25 and stops contributing at age 35 — investing for just 10 years. Total contributions: $60,000.
- Jordan starts at age 35 and invests $500/month all the way to age 65 — investing for 30 years. Total contributions: $180,000.
At 8% annual return, by age 65: Alex has ~$1,000,000 while Jordan has ~$750,000. Alex contributed one-third as much but ended up with more. That is the power of starting early.
How to Use This Calculator
Start with your current savings as "Initial Investment." Add what you can afford monthly. The default 8% reflects historical S&P 500 average returns (before inflation). Be realistic — don't assume 15% returns. A conservative 6-7% after inflation is a better planning number.
The Rule of 72
Want a quick estimate? Divide 72 by your annual return rate. At 8%, your money doubles every 9 years (72 / 8 = 9). At 10%, every 7.2 years. This mental shortcut helps you think in decades, not days.