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Compound Interest Calculator

See exactly how your money grows with compound interest — choose any compounding frequency and see the power of time.

✔ All Compounding Frequencies📐 Formula Shown

📈 Compound Interest Calculator

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The Power of Compound Interest

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Albert Einstein allegedly called it the "eighth wonder of the world" — whether or not he said it, the math is remarkable: $10,000 invested at 8% for 40 years grows to over $217,000 with no additional contributions.

📐 Compound Interest Formula

A = P(1 + r/n)^(n×t) + contributions
A= Final amount
P= Principal (initial investment)
r= Annual interest rate (decimal)
n= Compounding frequency per year
t= Time in years
📝 Example — $10,000 at 8% monthly for 20 years: A = $10,000 × (1 + 0.08/12)^(12×20)
A = $10,000 × (1.006667)^240
A = $10,000 × 4.9268 = $49,268

Frequently Asked Questions

Simple interest is calculated only on the principal: Interest = P × r × t. Compound interest is calculated on the principal plus all previously earned interest. Over long periods, compound interest grows exponentially while simple interest grows linearly. For a $10,000 investment at 8% over 30 years: simple interest = $24,000 profit; compound interest = $90,627 profit.
More frequent compounding produces slightly higher returns. Daily compounding versus annual compounding on $10,000 at 10% for 10 years: daily = $27,179; annual = $25,937 — a difference of $1,242. For most investors, the difference between daily and monthly compounding is negligible compared to factors like contribution amount and investment timeline.
$10,000 invested at 8% annual return compounded monthly grows to approximately $22,196 in 10 years, $48,980 in 20 years, and $107,651 in 30 years. The longer the time horizon, the more dramatic the compounding effect — over 30 years, nearly 90% of the final balance is interest on interest.
High-yield savings accounts (HYSA) at online banks currently offer 4–5% APY. CDs offer fixed rates up to 5% for terms of 6–18 months. For long-term compounding, index funds in a Roth IRA or 401(k) historically average 7–10% annually. The best account depends on your time horizon and liquidity needs.
⚠️ Disclaimer Estimates for informational purposes only. Not legal or financial advice. Consult a qualified professional.

What is Compound Interest and How Does it Work?

Compound interest is interest calculated on both the original principal and the accumulated interest from previous periods. Albert Einstein is often (though likely apocryphally) credited with calling it the "eighth wonder of the world" — its power lies in exponential growth: interest earns interest, which earns more interest, growing wealth faster over time.

Formula: A = P(1 + r/n)^(nt)
Where A = final amount, P = principal, r = annual rate, n = compounding frequency, t = time in years.

Compounding Frequency — Does It Matter?

CompoundingTimes/Year$10,000 at 5% after 10 years
Annually1$16,289
Quarterly4$16,436
Monthly12$16,470
Daily365$16,487

Daily compounding earns about $200 more than annual compounding over 10 years on $10,000 — meaningful on larger sums and longer timeframes. Most savings accounts and investment accounts compound daily or monthly.

The Rule of 72 — Quick Mental Math for Compound Growth

The Rule of 72 is a shortcut for estimating how long it takes to double your money: divide 72 by the annual interest rate. At 6% interest: 72 ÷ 6 = 12 years to double. At 8%: 9 years. At 4%: 18 years. It's remarkably accurate for rates between 4–20% and useful for quick mental comparisons.

Compound Interest vs Simple Interest

Simple interest is calculated only on the principal: I = P × r × t. Compound interest calculates on principal plus previous interest. Over short periods, the difference is small. Over decades, it's enormous: $10,000 at 7% simple interest for 30 years grows to $31,000. At 7% compound interest, it grows to $76,123 — more than 2.4× more.

How Regular Contributions Supercharge Compound Growth

Adding regular contributions (monthly or annual) dramatically accelerates compound growth. Investing $500/month at 7% annual return for 30 years results in $567,000 — from just $180,000 in total contributions. The extra $387,000 is entirely from compound interest. Starting 10 years earlier could nearly double the final amount. Time in the market is the most powerful variable.