How Compound Interest Works
Understand compound interest, the eighth wonder of the world, and how it helps your money grow over time.
What is Compound Interest?
Compound interest is interest calculated on the initial principal and also on the accumulated interest from previous periods. In simple terms, you earn interest on your interest, causing your money to grow exponentially over time.
Albert Einstein Called It
"The eighth wonder of the world. He who understands it, earns it; he who doesn't, pays it."
Compound Interest vs Simple Interest
Simple Interest:
Interest is calculated only on the principal amount. Example: $1,000 at 5% = $50/year, every year.
Compound Interest:
Interest is calculated on principal + previously earned interest. Example: $1,000 at 5% compounds to $1,050 (year 1), $1,102.50 (year 2), $1,157.63 (year 3), etc.
The Compound Interest Formula
A = P(1 + r/n)^(nt)
A = Final amount
P = Principal (initial amount)
r = Annual interest rate (decimal)
n = Number of times interest compounds per year
t = Time in years
Example: The Power of Compounding
$10,000 invested at 7% annual return:
| Year | Balance | Interest Earned |
|---|---|---|
| 0 | $10,000 | - |
| 5 | $14,025.52 | $4,025.52 |
| 10 | $19,671.51 | $9,671.51 |
| 20 | $38,696.84 | $28,696.84 |
| 30 | $76,122.55 | $66,122.55 |
Key Insight: In the first 10 years, you earn $9,671. In the next 20 years, you earn $56,451 - nearly 6x more, even though the time period is only 2x longer!
Factors That Affect Compound Interest
- Principal Amount: More money = more growth
- Interest Rate: Higher rate = faster growth
- Time: Longer time = exponential growth
- Compounding Frequency: More frequent compounding (monthly vs annually) = slightly more growth
- Regular Contributions: Adding money regularly accelerates growth significantly
How to Maximize Compound Interest
- Start early: Time is the most powerful factor
- Invest regularly: Monthly contributions compound over time
- Reinvest earnings: Don't withdraw interest - let it compound
- Choose higher rates: Compare investment options
- Be patient: Compound interest works best over long periods
Calculate Your Compound Interest
Use our Compound Interest Calculator to see how your money grows over time.
Try the Calculator
Compound Interest Calculator
Calculate how your investment grows over time with compound interest. See the final amount, total contributions, and interest earned.
How to: Define your initial investment amount - the starting balance you invest today
Investment Calculator
Estimate how your investments grow over time with compound returns. Calculate profit, total contributions, and long-term value.
How to: Enter your initial investment - the starting amount you invest today (can be $0)
Savings Calculator
Plan your savings and see how regular deposits grow over time. Calculate savings growth with compound interest.
How to: Enter your initial savings - the amount you already have saved (can be $0)