Compound Interest Explained: Why Starting Early Beats Saving More

What compound interest really means

Compound interest is interest earned on your interest. In year one you earn a return on your principal. In year two you earn a return on the principal plus year one's gains. Over decades this creates an accelerating snowball — the curve bends upward rather than rising in a straight line.

The rule of 72

Want a quick estimate of how long it takes your money to double? Divide 72 by your annual return. At 8%, money doubles roughly every 9 years (72 ÷ 8). At 6%, every 12 years. It is a handy mental shortcut for the power of compounding.

Why time beats contribution size

Consider two investors earning 7% a year. Alex invests $200/month from age 25 to 35, then stops — $24,000 total. Jordan waits until 35 and invests $200/month until 65 — $72,000 total. At 65, Alex often ends up with a similar or larger balance despite investing a third as much, purely because the early money compounded for 40 years.

The lesson: the most valuable ingredient in investing is time, not timing or amount.

Make it automatic

• Start now, even with a small amount — time in the market matters most.
• Automate monthly contributions so you never skip a month.
• Reinvest dividends and returns to keep the snowball rolling.
• Use tax-advantaged accounts (401k, IRA) to compound without the tax drag.