Compound Interest Calculator
See how your money grows with compound interest and optional recurring contributions — with a full year-by-year breakdown.
No uploads • No tracking • No registration
Assumptions: this calculator assumes a constant annual interest rate compounded at the frequency you select, with any recurring contribution added at the end of each compounding period before the next period's interest is calculated. Real investments rarely grow at a perfectly constant rate — this is a projection, not a guaranteed return.
How It Works
Enter your numbers
Principal, rate, time period and an optional recurring contribution.
Choose a compounding frequency
Annually, semi-annually, quarterly, monthly or daily.
See the growth breakdown
Final balance, total interest, and a year-by-year table and chart.
Privacy note: every calculation runs locally in your browser. Your financial figures are never sent to a server.
The formula
A = P(1 + r/n)ⁿᵗ + C × [((1 + r/n)ⁿᵗ − 1) ÷ (r/n)]
P is the principal, r the annual rate, n the compounding periods per year, t the time in years, and C the contribution added each period. Without contributions (C = 0), this reduces to the standard compound interest formula A = P(1 + r/n)ⁿᵗ.
Frequently Asked Questions
What is the compound interest formula?+
A = P × (1 + r/n)^(n×t), where P is the initial principal, r is the annual interest rate, n is how many times per year interest compounds, and t is the time in years. This calculator extends the formula to also account for a recurring contribution added at the end of each compounding period.
How are recurring contributions handled?+
Contributions are added at the end of each compounding period, at the same frequency you select for compounding. For example, with monthly compounding, a contribution amount is added once per month, and it starts earning interest from the following period.
Does compounding frequency actually make a meaningful difference?+
Yes, though the effect shrinks as frequency increases. Daily compounding produces a slightly higher balance than monthly, which is slightly higher than quarterly, and so on, because interest starts earning its own interest sooner. The difference is usually modest for typical rates and time periods.
What's the difference between total contributions and total interest earned?+
Total contributions is simply the sum of your initial principal and every recurring contribution you made, with no growth applied. Total interest earned is the final balance minus that sum — the actual amount your money grew by.
Is this calculator accurate for real investment returns?+
The math is accurate for the fixed rate and compounding assumptions you enter. Real investments (stocks, funds, savings accounts) rarely grow at a perfectly constant rate, so this is a projection based on a constant assumed rate, not a guarantee or prediction of actual returns.
Can I model a lump sum with no ongoing contributions?+
Yes. Leave the contribution field at zero or blank to calculate pure compound growth on your initial principal alone.
Does this tool store my financial figures?+
No. All calculations happen locally in your browser using JavaScript. Nothing you enter is sent to a server or saved.