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About Compound Interest Calculator Online
This tool computes the future value of an investment or savings account that earns compound interest. You provide the principal, annual interest rate, compounding frequency (daily, monthly, quarterly, semi-annually, or yearly), and the investment duration, and the calculator returns the final balance, total interest earned, and the year-by-year growth.
Compound interest is the engine behind long-term wealth building. Unlike simple interest, which only pays on the original principal, compound interest pays interest on previously accrued interest — meaning the longer you let the money grow, the faster the balance climbs. The same calculation works for retirement accounts, certificates of deposit, dividend reinvestment plans, and high-yield savings.
If you contribute additional money each period, enable the recurring deposit option. The calculator will compound both the principal and your contributions, giving you a realistic view of how a habitual saving plan plays out over years or decades.
How to use this tool
How to project compound interest over N periods
Set the starting balance
"Initial amount" is the principal applied before any interest. Range is 1e-12 to 1e15 — works for cents to trillions. No deposits/withdrawals are modelled; assume a single up-front lump sum.
Enter rate per period
"Interest rate per period (%)" is the percentage applied at the start of each step (e.g. 5 = 5% per period). Negative rates work (deflation / managed-loss scenarios). Range: -100 to 500.
Choose how many steps
"Number of periods (steps)" is the count of compounding rows produced (1–500, default 12). Each row is one period — annual / quarterly / monthly depends on the rate you entered.
Press Run
Result returns stepSchedule (per-row balance, interest, total), plus futureValue and totalInterest summaries. Copy the schedule into a spreadsheet to compare scenarios with different rates.