📈 Compound Interest Calculator
Enter a starting principal, an annual rate, a term, a compounding frequency, and an optional regular contribution to see the projected future value, everything you contributed, and the interest earned.
🧮 Project Compound Growth
What is a Compound Interest Calculator?
It shows how money can grow when returns are reinvested and left to compound. Enter what you start with, the rate, how long you leave it, and how often interest is applied — plus anything you add each period — and it projects the ending balance, separates out what you contributed, and shows the interest that compounding added on top.
It's a classic tool for understanding why time and reinvestment matter, but the projection assumes a steady rate that real investments rarely deliver. The figures are an illustration of the arithmetic, not a forecast or a recommendation to invest.
❓ Frequently Asked Questions
How is compound interest calculated?
The lump sum grows by the formula principal × (1 + i)^N, where i is the periodic rate (annual rate ÷ compounding periods per year) and N is the total number of periods. Regular contributions are grown with the future-value-of-an-annuity formula and added on. The tool then reports the future value, everything you put in, and the difference as interest.
What does compounding frequency change?
It's how often interest is added to the balance so it can itself earn interest. For the same annual rate, more frequent compounding (monthly vs annual) produces a slightly larger future value. This is why the effective yield can exceed the stated rate.
Are these projections guaranteed?
No. The calculator assumes a fixed rate and that all interest is reinvested. Real-world returns fluctuate, may be negative, and are reduced by taxes and inflation. Treat the output as an illustration of the maths, not a promise of results.
Is this financial advice?
No. This calculator is for educational and informational purposes only and does not recommend any investment. Investing involves substantial risk of loss; consult a licensed financial advisor before making decisions.