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How Compound Interest Works (And Why It Matters)

15 Aug 2024
5 min read

Einstein supposedly called it the eighth wonder of the world. Here's how compound interest turns small, regular investments into serious wealth over time.


What Is Compound Interest?

Compound interest is interest earned on your interest. Instead of just earning returns on your original investment, you earn returns on your returns too. Over time, this creates a snowball effect.

Simple vs Compound Interest

Let's say you invest $10,000 at 7% per year:

Simple Interest (no compounding)


  • Year 1: $10,000 + $700 = $10,700

  • Year 2: $10,000 + $700 = $11,400

  • Year 10: $10,000 + $7,000 = $17,000

    • You earn $700 every year, always calculated on the original $10,000.

    Compound Interest


  • Year 1: $10,000 + $700 = $10,700

  • Year 2: $10,700 + $749 = $11,449

  • Year 10: $10,000 grows to $19,672

    • The difference? $2,672 extra — and that gap gets wider every year.

    The Magic of Time

    The real power of compounding is time. The earlier you start, the more dramatic the results:

    Starting at age 25 vs 35 (investing $200/month at 7%)

  • Start at 25, retire at 60: ~$340,000

  • Start at 35, retire at 60: ~$152,000

    • Starting just 10 years earlier more than doubles your result — even though you only contributed an extra $24,000.

    The Rule of 72

    Want a quick way to estimate how long it takes to double your money? Divide 72 by your annual return rate:

  • At 5% return: 72 / 5 = 14.4 years to double

  • At 7% return: 72 / 7 = 10.3 years to double

  • At 10% return: 72 / 10 = 7.2 years to double

    • How to Make Compounding Work for You

  • Start now - Even small amounts benefit from more time in the market

  • Be consistent - Regular contributions matter more than timing the market

  • Reinvest dividends - Let your returns compound rather than cashing them out

  • Keep fees low - High fees eat into your compounding returns every year

  • Be patient - Compounding is slow at first and explosive later. Don't give up early.

    • See It in Action

    Use the Growth Projector in Citrafort to see exactly how your Growth contributions could grow over 5, 10, 20, or 30 years at different return rates.