📈 Compound Interest Calculator
Calculate how your money grows with compound interest. See a year-by-year breakdown of your investment growth — all in your browser.
What Is Compound Interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. It's often called "interest on interest" and is the reason investments can grow exponentially over time. Albert Einstein reportedly called it "the eighth wonder of the world."
The formula is: A = P(1 + r/n)nt
Where A = future value, P = principal, r = annual rate, n = compounds per year, t = years.
How to Use This Tool
- Enter your initial investment amount.
- Enter any monthly contribution you plan to add regularly.
- Set the annual interest rate and investment period.
- Choose the compounding frequency (daily, monthly, quarterly, etc.).
- Click Calculate to see your projected growth.
Why Use This Tool?
- Visualize the power of compound interest over time.
- Plan retirement savings, education funds, or investment goals.
- Compare different compounding frequencies and contribution amounts.
- All calculations run in your browser — your financial data stays private.
Frequently Asked Questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the initial principal, while compound interest is calculated on the principal plus any accumulated interest. Compound interest grows exponentially, while simple interest grows linearly.
How often should interest compound?
More frequent compounding (daily vs. annually) results in slightly more interest earned. For most savings accounts, monthly or daily compounding is standard. The difference becomes more significant with larger amounts and longer time periods.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by the annual interest rate. For example, at 8% interest, your money doubles in approximately 72/8 = 9 years.