Free Compound Interest Calculator

The Compound Interest Calculator is a free online tool that projects investment growth with compound interest, showing how your money grows over time with regular contributions.

Yes, it is completely free with no registration required. All calculations happen client-side in your browser.

Yes, the Compound Interest Calculator lets you add monthly or annual contributions to see their impact on your total investment growth.

Absolutely. The Compound Interest Calculator processes everything client-side in your browser. No data is uploaded to or stored on any server. Your content remains private on your device at all times.

Yes, the Compound Interest Calculator is fully responsive and works on smartphones and tablets. You can use it on any device with a modern web browser -- no app download required.

No account or registration is needed. Simply open the Compound Interest Calculator in your browser and start using it immediately. There are no sign-up walls or usage restrictions.

The Compound Interest Calculator uses industry-standard formulas and algorithms to ensure accurate results. However, for critical financial or medical decisions, always consult a qualified professional.

Simply enter your input in the provided field, adjust any settings to your preference, and the tool will process it instantly. You can then copy the result to your clipboard or download it.

The Compound Interest Calculator works in all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. For the best experience, use the latest version of your preferred browser.

Simple interest is calculated only on your original principal, so a $10,000 deposit at 5% earns a flat $500 every year regardless of how long you hold it. Compound interest is calculated on the principal plus all previously earned interest, so each year's interest is added to the balance and starts earning interest itself. That snowball effect is small early on but grows dramatically over long periods — the gap between the two widens every year. The longer your time horizon and the higher the rate, the more compounding pulls ahead of simple interest. This calculator's Overview contrasts compound growth against plain simple interest side by side, so you can see exactly how many extra dollars compounding adds over your full term. Enter a principal, rate, and number of years to compare them instantly.

Compounding frequency is how often earned interest is added back to your balance so it can start earning more. The more often this happens, the higher your effective return from the same stated rate, because interest begins compounding sooner. A 7% annual rate compounded monthly produces a slightly higher effective yield than the same 7% compounded once a year, while daily and continuous compounding add only a small fraction more on top of that — the gains shrink as frequency rises. This tool supports seven frequencies: annually, semi-annually, quarterly, monthly, weekly, daily, and continuous, using the formula A = P(1 + r/n)^(nt). The Compare view lists them side by side so you can see precisely what each one is worth. Select your frequency above to see how it affects your projected balance.

APY, or annual percentage yield, is the rate you actually earn over a year once compounding is factored in, while the stated or nominal interest rate ignores compounding. For any frequency more often than yearly, the APY is higher than the nominal rate. For example, a 6% nominal rate compounded monthly works out to an effective yield slightly above 6% because each month's interest earns interest for the rest of the year. APY is the fairest way to compare accounts, since a higher nominal rate with annual compounding can lose to a lower rate that compounds daily. This calculator reports the effective annual yield alongside your final balance, so you can judge accounts on equal terms. Enter your rate and compounding frequency to see the true APY behind the numbers.

A quick estimate comes from the Rule of 72: divide 72 by your annual interest rate to approximate the number of years it takes an investment to double. At 6% your money roughly doubles in 12 years (72 / 6), at 8% in about 9 years, and at 4% in around 18 years. The rule is an approximation that works best for rates between about 4% and 12%; outside that band it drifts slightly from the exact figure derived from logarithms. It also assumes a fixed rate and no withdrawals. This calculator surfaces a Rule of 72 doubling estimate right in the Overview, and the year-by-year timeline shows the actual balance climbing so you can see when it crosses double. Enter your rate to get your doubling time at a glance.

Working backward from a target is its own calculation: instead of projecting a balance forward, you solve for the monthly contribution needed to hit a specific number by a certain date. The inputs are your target amount, your starting balance, an expected annual rate, and a timeframe — the math then accounts for both your principal growing and each contribution compounding over the remaining years. A longer horizon or higher rate lowers the monthly amount required, since compounding does more of the work for you. This tool has a dedicated Goal mode that flips the standard projection and reports the exact monthly contribution to reach your target, whether that's a down payment, an emergency fund, or a retirement figure. Switch to Goal mode, enter your target and timeframe, and it solves for the deposit you need.