Compound Interest Calculator
See how your money grows over time with compound interest. Enter your initial investment, interest rate, time period, and monthly contributions to get a detailed breakdown with interactive charts.
How to Use
- 1 Enter your initial investment (principal) amount in the first field
- 2 Set the annual interest rate as a percentage (e.g., 7% for average stock market returns)
- 3 Choose the time period in years for your investment horizon
- 4 Optionally add monthly contributions to see how regular deposits accelerate growth
- 5 Select the compounding frequency (monthly, quarterly, or annually) to match your investment type
- 6 View the results instantly: future value, total interest earned, and a year-by-year breakdown chart
What You Get
Free online compound interest calculator with visual growth chart. Calculates future value, total interest earned, and effective annual rate for savings and investments. Supports monthly contributions and multiple compounding frequencies (monthly, quarterly, semi-annually, annually). Shows year-by-year breakdown with principal vs. interest visualization. 100% client-side — no data sent to any server.
Input: $10,000 at 7% for 30 years (monthly compounding)
Output: $81,165 (total interest: $71,165)
Input: $5,000 + $200/month at 5% for 20 years
Output: $96,112 (contributions: $53,000, interest: $43,112)
Input: $1,000 at 10% for 10 years, monthly compounding
Output: $2,707 (interest earned: $1,707)
What is compound interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (which only earns interest on the original amount), compound interest grows exponentially because you earn "interest on interest." For example, $1,000 at 10% simple interest earns $100/year forever, but with compound interest, year 2 earns $110 (10% of $1,100), year 3 earns $121, and so on.
What is the compound interest formula?
The basic compound interest formula is A = P(1 + r/n)^(nt), where A is the future value, P is the principal (initial investment), 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. For example, $10,000 at 5% compounded monthly for 10 years: A = 10000(1 + 0.05/12)^(12×10) = $16,470.09.
How often should interest be compounded?
The more frequently interest is compounded, the more you earn. Monthly compounding earns slightly more than quarterly, which earns more than annually. However, the difference is often small. For example, $10,000 at 5% for 10 years: annually = $16,288.95, quarterly = $16,436.19, monthly = $16,470.09. Most savings accounts compound daily or monthly, while many investments compound annually.
What is a good compound interest rate?
Interest rates vary by investment type. High-yield savings accounts currently offer 4-5% APY. The historical average annual return of the S&P 500 stock market index is about 10% (7% after inflation). Government bonds typically yield 3-5%. CDs (Certificates of Deposit) offer 4-5%. The "Rule of 72" is a quick shortcut: divide 72 by your interest rate to estimate how many years it takes to double your money (e.g., 72 ÷ 7% ≈ 10.3 years).
How do monthly contributions affect compound interest?
Regular monthly contributions dramatically accelerate wealth building due to dollar-cost averaging and compound growth. For example, $10,000 invested at 7% for 30 years with monthly compounding grows to $81,165. But adding just $200/month turns it into $326,582 — the extra $72,000 in contributions generates over $173,000 in additional interest. This is why financial advisors recommend automated monthly investing.
What is the difference between APR and APY?
APR (Annual Percentage Rate) is the simple annual rate without compounding. APY (Annual Percentage Yield) includes the effect of compounding and shows what you actually earn. For example, a 5% APR compounded monthly has an APY of 5.116%. APY is always equal to or higher than APR. Banks advertise APY for savings (looks higher) and APR for loans (looks lower). This calculator uses the annual rate (APR) and shows you the effective APY.
Is this compound interest calculator accurate?
Yes. This calculator uses the standard compound interest formula with IEEE 754 double-precision floating-point arithmetic, rounded to 2 decimal places for currency display. It accounts for compounding frequency and monthly contributions precisely. All calculations run entirely in your browser with no rounding shortcuts. For tax planning or official financial decisions, always consult a financial advisor.
Is this calculator free?
Yes, this compound interest calculator is 100% free with no account required. All calculations run in your browser — no data is sent to any server. There are no ads, no usage limits, and no premium features locked behind a paywall.
All calculations run in your browser. Nothing is sent to any server.