Compound Interest Calculator

WHAT IT DOES

Compound Interest Calculator shows you how your money grows over time through the power of compounding. Enter your principal amount, annual interest rate, choose from five compounding frequencies (annually, semi-annually, quarterly, monthly, or daily), and set your investment time period. The panel instantly displays your final balance, total interest earned, and the growth multiplier. A detailed year-by-year breakdown shows exactly how your investment grows each year, with a special indicator for partial years. This clear visualization helps you understand the impact of compounding frequency and time on investment growth.

WHERE IT RUNS

This script runs on every website you visit. Whether you are planning retirement savings on financial planning sites, comparing investment options on brokerage platforms, evaluating savings accounts on bank websites, or working with investment scenarios in a spreadsheet application, the panel is always available. It works alongside your existing tools without interfering with your workflow.

HOW TO USE

Enter your principal amount in the first field, the annual interest rate as a percentage in the second field, select your compounding frequency from the dropdown menu, and enter the time period in years. Results update automatically as you type. Scroll through the year-by-year breakdown to see how your balance grows over time — each year shows the balance and interest earned to date. Partial years are displayed with a highlighted row for precise calculations. Click any history entry to reload previous calculations for quick comparisons. Use the "Copy Result" button to copy the final balance and total interest to your clipboard.

THE COMPOUNDING PRECISION MECHANISM

Compound Interest Calculator uses the standard compound interest formula: A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate, n is the number of compounding periods per year, and t is the time in years. The calculator handles partial years correctly — if you enter 5.5 years, it compounds for exactly 5.5 periods using the fractional exponent, giving you precise results rather than rounding down to whole years. All financial values are rounded to two decimal places using standard rounding rules, and the year-by-year breakdown shows the cumulative growth at each interval. The calculator supports up to 50 years of detailed breakdown, with an indicator for months beyond the first 60 if applicable.

THE PANEL

The panel is fully draggable and remembers its position per site. It minimizes to a compact floating bubble when collapsed. All settings — default interest rate, default compounding frequency, default time period, and calculation history — persist across browser sessions using GM_setValue storage. Press the Escape key to close the panel. The panel automatically focuses the principal input field for quick keyboard entry.

PLEASE NOTE

This script requires the free BotGentz extension to run. The calculations are estimates based on standard compound interest formulas — actual investment returns vary and are not guaranteed. Historical performance does not predict future results. Always consult with a qualified financial advisor before making investment decisions. Websites change their structure and behavior over time; if any functionality stops working, the script may need an update. No user data is sent anywhere — all calculation history and settings are stored locally in your browser. The script never reads or modifies password, hidden, or file input fields.