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Compound Interest calculator →

Compound Interest guide

The Compound Interest Calculator projects the future value of an investment based on an initial principal, an annual interest rate, the compounding frequency, and regular monthly contributions.

Worked examples

Calculate basic compound growth

  1. Enter $10,000 as the Initial Principal.
  2. Enter 5% as the Annual Interest Rate.
  3. Set Time to 10 Years.
  4. Set Monthly Contribution to $0.
  5. Set Compounding Frequency to Monthly.
Result: Future Value ≈ $16,470.09

Without adding extra money, the initial $10k grows by 5% annually, compounded monthly, over 10 years.

Calculate growth with monthly contributions

  1. Enter $1,000 as the Initial Principal.
  2. Enter 7% as the Annual Interest Rate.
  3. Set Time to 30 Years.
  4. Set Monthly Contribution to $100.
Result: Future Value ≈ $129,328.28

Adding $100 every month accelerates growth dramatically due to compound interest on the contributions themselves.

Compare Annual vs Daily Compounding

  1. Enter $10,000, 5% interest, 10 years.
  2. First, calculate with Annual compounding.
  3. Then, change to Daily compounding and calculate again.
Result: Annual ≈ $16,288.95 | Daily ≈ $16,486.65

The more frequently interest is compounded, the higher the final yield.

Tips

  • •Start early. Time is the most powerful variable in compound interest.
  • •Use the Rule of 72 to estimate how long it takes to double your money: 72 / interest rate = years to double.
  • •Monthly contributions are applied at the end of each month in this model.

Frequently asked questions

What is compound interest?
Interest calculated on both the initial principal and the accumulated interest from previous periods.
What is the difference between simple and compound interest?
Simple interest is calculated only on the principal. Compound interest grows exponentially because you earn interest on your interest.
What is the Rule of 72?
A mental math shortcut. Divide 72 by your annual interest rate to find the approximate number of years it takes for your money to double.
What is compounding frequency?
How often interest is calculated and added to your balance (annually, monthly, daily).
Why does more frequent compounding yield more money?
Because interest starts earning its own interest sooner.
What is APY?
Annual Percentage Yield. It is the actual rate of return you will earn in one year, accounting for the effect of compounding.
What is the difference between APR and APY?
APR is the nominal rate without compounding. APY includes compounding. APY will always be higher or equal to APR.
Are my monthly contributions added at the beginning or end of the month?
In this calculator, contributions are added at the end of each month.
Can I calculate continuous compounding?
The tool supports daily compounding, which is extremely close to continuous compounding.
What happens if I enter a negative interest rate?
The calculator will show the value decreasing over time, simulating deflation or an investment loss.
How do I account for inflation?
Subtract the expected inflation rate from your annual interest rate to find the "real" return.
What is the principal?
The initial amount of money you invest or deposit.
Why is the total interest so high after 30 years?
Because of exponential growth. The longer the time horizon, the more dramatic the curve becomes.
What is a 401(k)?
A retirement savings account in the US that relies heavily on compound interest over decades.
Does the calculator include taxes or fees?
No. It shows the gross future value. Taxes and fund management fees will reduce the final amount.
Can I use this for a loan?
Yes, but the math works against you. A loan accrues compound interest that you must pay.
What is a realistic interest rate to expect?
Historically, the stock market averages around 7-10% annually (before inflation), while savings accounts offer 1-5%.
Are the results exact?
Results are estimates rounded to the nearest cent, assuming consistent contributions and no missed payments.
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