📈 Compound Interest Calculator
Enter a starting amount, return rate, time and monthly contribution to see the future value, with the interest earned and a growth chart.
Future value
$144,573
You contributed
$58,000
Interest earned
$86,573
Interest share
60%
FV = P(1+i)ⁿ + contributions × [((1+i)ⁿ−1)/i]. Educational estimate, not investment advice; real returns vary. 🔒 In your browser.
How the compound interest calculator works
Compound interest earns returns on your returns. The future value is FV = P(1+i)ⁿ for the lump sum, plus a contributions term for regular deposits: contribution × [((1+i)ⁿ − 1) / i], where i is the periodic rate and n the number of periods. The periodic rate i is the annual rate divided by the number of compounds per year, and n is the number of years times that same frequency, so a 6% annual rate compounded monthly means i = 0.005 and n = 12 per year. The tool adds the lump-sum and contribution terms together, and shows how much of the total you contributed versus how much came purely from growth.
The rate you enter is assumed constant, real investment returns vary year to year, so treat the result as an illustration, not a promise. This is an educational tool, not financial advice.
Frequently asked questions
How does compound interest work?
You earn interest on your original money and on the interest already added, so growth accelerates over time. FV = P(1+i)ⁿ; with regular deposits you add an annuity term for the contributions.
How do I include monthly contributions?
Enter a monthly deposit and the tool adds the future value of that stream: contribution × [((1+i)ⁿ − 1) / i]. Regular investing is what drives most long-term growth.
What does compounding frequency change?
More frequent compounding (daily vs annually) slightly increases the result because interest is added and starts earning sooner. The difference is small at typical rates.
Why does starting early matter so much?
Because compounding is exponential, an extra decade lets the interest compound on itself far longer. A small amount invested early often beats a larger amount invested late.
Is the projected return guaranteed?
No. The calculator assumes a fixed rate; actual markets fluctuate. Use it to compare scenarios, not as a guarantee. It is educational, not financial advice.
What is the difference between simple and compound interest?
Simple interest is always calculated on the original principal, so it grows in a straight line. Compound interest is calculated on the principal plus all previously earned interest, so it grows exponentially, the gap between the two widens the longer you invest.
How do I work out how much I actually earned?
Subtract everything you put in (starting amount plus all contributions) from the future value. The tool splits this out for you, showing total contributions separately from interest earned so you can see how much of the balance is growth.
Educational information, not financial advice. These calculators use standard formulas with the figures you enter; results are illustrations, not guarantees. For decisions about your money, consult a qualified, regulated financial professional.