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Compound Interest Calculator

See how your money grows with compound interest and regular contributions.

Frequently Asked Questions

What is compound interest?

Compound interest is interest calculated on the initial principal and also on the accumulated interest from previous periods.

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๐Ÿ“Š Data Summary (auto-filled)

Tool: Compound Interest Calculator ยท /tools/compound-interest/

compounding: monthly

contribFreq: monthly

What is this tool?

Compound interest is the interest calculated on the initial principal and also on the accumulated interest from previous periods. It causes money to grow at an accelerating rate over time, famously described by Einstein as the eighth wonder of the world. The formula is A = P(1 + r/n)^(nt), where P is principal, r is annual rate, n is compounding frequency, and t is time in years.

When to use this tool

  • Long-term investment planning

    Model how regular contributions grow over decades. See why starting your investment early โ€” even with smaller amounts โ€” dramatically increases your final wealth.

  • Savings vs. investment comparison

    Compare the growth of a high-yield savings account vs. an index fund. Over 20 years, the difference in returns can be hundreds of thousands of dollars.

  • Retirement estimation

    Estimate how your retirement savings will grow. Use the calculator to see the impact of starting to contribute at age 25 vs. age 35.

How to use

  1. 1

    Enter initial principal

    Type the starting amount of money you will invest.

  2. 2

    Set annual interest rate

    Enter the expected annual return rate as a percentage.

  3. 3

    Choose compounding frequency

    Select how often interest is compounded: annually, semi-annually, quarterly, monthly, or daily.

  4. 4

    Set investment period

    Enter the number of years you plan to invest.

  5. 5

    View growth breakdown

    See final amount, total interest earned, and year-by-year growth breakdown.

Frequently Asked Questions

What is the Rule of 72?

The Rule of 72 is a quick way to estimate how long it takes for an investment to double. Divide 72 by the annual interest rate. For example, at 8% annual return, your money doubles in approximately 72/8 = 9 years.

How often should interest compound for best results?

More frequent compounding yields slightly higher returns, but the difference diminishes. Daily compounding earns about 0.25% more than annual. In practice, the investment return rate matters far more than compounding frequency.

Can compound interest work against me?

Yes. Credit card debt uses compound interest against you. High-interest debt compounds daily, meaning unpaid balances grow exponentially. A $1,000 balance at 20% APR can double in less than 4 years if only minimum payments are made.

How much will $1,000 grow with compound interest?

At 7% annual return compounded monthly: $1,000 grows to approximately $2,000 in 10 years, $4,400 in 20 years, $10,600 in 30 years, and $76,000 in 50 years. This demonstrates why starting early is the most powerful factor in long-term investing โ€” time is more important than the amount invested.

What is the difference between simple and compound interest?

Simple interest is calculated only on the original principal. Compound interest is calculated on principal plus previously accumulated interest. For $1,000 at 5% over 10 years: simple interest = $500 total, compound interest = $629. The difference becomes dramatically larger over longer periods and higher rates. Einstein reportedly called compound interest the eighth wonder of the world.

What is compound interest?

Compound interest is interest that earns interest: instead of being paid only on your original deposit, it is added to the balance and becomes part of the principal that future interest is calculated on. The effect grows exponentially over time: the longer you invest and the more often interest compounds, the faster the balance grows. This is why starting early matters more than starting big.

How do I calculate compound interest with the standard formula?

Use A = P ร— (1 + r/n)^(nยทt): P is the principal, r the annual rate as a decimal, n the number of compounding periods per year, and t the number of years. For $10,000 at 5% compounded monthly over 10 years: A = 10000 ร— (1 + 0.05/12)^(12ร—10) โ‰ˆ $16,470.

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