# Compound Interest Calculator Calculate compound interest on investments and savings. See how your money grows with different rates, terms, and compounding frequencies. ## What this calculates Discover the power of compound interest with our free calculator. Enter your initial investment, interest rate, time period, and compounding frequency to see how your money grows. Optionally add monthly contributions to see how regular investing accelerates wealth building. ## Inputs - **Initial Investment (Principal)** ($) — min 0 — The starting amount of your investment. - **Annual Interest Rate** (%) — min 0, max 100 — The expected annual rate of return. - **Time Period (years)** — min 0, max 100 — How long you plan to invest. - **Compounding Frequency** — options: Annually, Semi-annually, Quarterly, Monthly, Daily — How often interest is compounded. - **Monthly Contribution** ($) — min 0 — Additional amount you invest each month (optional). ## Outputs - **Future Value** — formatted as currency — The total value of your investment at the end of the term. - **Total Contributions** — formatted as currency — The total amount you invested (principal + contributions). - **Total Interest Earned** — formatted as currency — The total amount earned from compound interest. - **Effective Annual Rate (APY)** — formatted as percentage — The actual annual return after accounting for compounding frequency. ## Details Compound interest is often called the eighth wonder of the world. Unlike simple interest, which is calculated only on the principal, compound interest earns interest on both the original principal and the accumulated interest from previous periods. The formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate (as a decimal), n is the number of times interest is compounded per year, and t is the number of years. The frequency of compounding matters. The more frequently interest is compounded, the more you earn. For example, $10,000 at 7% for 10 years produces $19,672 with annual compounding but $20,097 with daily compounding -- a difference of $425 from compounding alone. Regular monthly contributions dramatically amplify the effect of compounding. Starting with $10,000 and adding $200 per month at 7% for 30 years grows to approximately $283,000. Without the monthly contributions, the same initial investment would only reach about $76,000. The key lesson: consistent investing over time is more powerful than a large one-time investment. The Rule of 72 provides a quick approximation: divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 7%, your money roughly doubles every 10.3 years. ## Frequently Asked Questions **Q: What is compound interest?** A: Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. This creates exponential growth over time, as you earn interest on your interest. For example, $1,000 at 10% annual compound interest becomes $1,100 after year one, then $1,210 after year two (10% of $1,100, not just 10% of $1,000). The formula is A = P(1 + r/n)^(nt). **Q: How does compounding frequency affect my returns?** A: More frequent compounding produces slightly higher returns because interest begins earning interest sooner. Daily compounding yields more than monthly, which yields more than quarterly, which yields more than annually. However, the differences become smaller as frequency increases. The jump from annual to monthly compounding is meaningful, but from monthly to daily is relatively small. **Q: What is the Rule of 72?** A: The Rule of 72 is a quick mental math shortcut to estimate how long it takes for an investment to double. Divide 72 by the annual interest rate to get the approximate number of years. At 6% interest, your money doubles in about 12 years (72/6). At 8%, it doubles in about 9 years (72/8). At 12%, it doubles in about 6 years (72/12). This is an approximation that works best for rates between 2% and 15%. **Q: What is the difference between APR and APY?** A: APR (Annual Percentage Rate) is the stated annual interest rate without accounting for compounding. APY (Annual Percentage Yield) is the effective annual rate that includes the effect of compounding. APY is always equal to or greater than APR. For example, a 6% APR compounded monthly has an APY of approximately 6.168%. When comparing savings accounts or investments, APY gives you the true annual return. **Q: How much should I invest monthly to become a millionaire?** A: It depends on your time horizon and expected return. Assuming a 7% average annual return (roughly the historical stock market average after inflation): starting from $0, you would need to invest about $381 per month for 40 years, $820 per month for 30 years, $2,048 per month for 20 years, or $5,776 per month for 10 years to reach $1 million. Starting earlier dramatically reduces the monthly amount needed. --- Source: https://vastcalc.com/calculators/finance/compound-interest Category: Finance Last updated: 2026-04-21