What Is Compound Interest?
📷 Compound interest turns small, consistent investments into life-changing wealth over time
Compound interest is earning interest on your interest — making money grow faster and faster the longer you leave it.
Compound interest has been called the most powerful force in the universe. The math is genuinely staggering — a single dollar invested wisely at 20 can become dozens of dollars by retirement without you ever adding another cent. The secret ingredient nobody can manufacture later is time.
You invest $1,000 at 10% per year
Starting point is the same either way.
Simple interest: earn $100 every year
After 20 years: $3,000. Predictable and flat.
Compound: earn 10% on growing balance
Year 2 earns on $1,100. Year 3 on $1,210. It accelerates.
Compound result after 20 years: $6,727
More than double — same money, same rate, same time.
Compound interest works both ways. It builds wealth when you're the investor — and drains it fast when you're the borrower. Credit card debt at 20% annual interest, left unpaid, compounds devastatingly.
Amy leaves $3,000 on her credit card at 20% interest, paying only the minimum. After 5 years she's paid over $2,800 in interest — and still owes close to $2,000. The original $3,000 purchase has cost nearly $5,800. Compound interest, working against her.
Divide 72 by your interest rate to find how long it takes to double your money. At 6%, your money doubles in 12 years. At 9%, just 8 years. At 12%, only 6 years. This makes compound interest instantly tangible.
🚫 Waiting to start. Someone who invests $200/month from age 22 to 32 — then stops — ends up with MORE money at retirement than someone starting at 32 and investing all the way to 65. Starting a decade earlier, with less total money invested, wins. Every year you wait, you lose compounding time you can never recover.
⚡ Quick Summary
Compound interest = earning interest on previous interest
Time is the most important variable — start early, benefit enormously
Works for investors, against borrowers — know which side you're on
Rule of 72: divide 72 by rate to find your doubling time