The Power of Compound Interest Explained

Compound interest is the single most powerful force in building long-term wealth. Understanding it changes how you think about saving and investing.

Simple vs. Compound Interest

Simple interest is calculated only on the original principal. $10,000 at 7% = $700/year, every year.

Compound interest earns interest on interest. Year 1: $700. Year 2: $749. Year 3: $801. It accelerates.

$10,000 at 7% for 30 years: Simple = $31,000. Compound = $76,123. A $45,000 difference from the same investment.

The Rule of 72

Divide 72 by your annual return to estimate doubling time:

• 6% return: 12 years to double
• 8% return: 9 years to double
• 10% return: 7.2 years to double

Why Starting Early Wins

Two investors, both earning 8% annually:

• Investor A: Starts at 25, invests $300/month for 10 years, stops. Total: $36K invested.
• Investor B: Starts at 35, invests $300/month for 30 years. Total: $108K invested.

At 65: A has $472K. B has $440K. Despite investing 3x less, A wins — purely from a 10-year head start.

How to Maximize Compound Growth

1. Start as early as possible
2. Be consistent — regular contributions beat timing
3. Reinvest dividends
4. Minimize fees — 1% costs tens of thousands over a career
5. Use tax-advantaged accounts

The Bottom Line

Compound interest rewards patience. Use our retirement calculator to see how your savings compound over time.