Compound Interest Calculator
See how your money grows when interest earns interest. Add a starting amount, a monthly deposit and a yearly rate to see your balance year by year.
Your result appears here.
By Shah Rukh, software developer · Last updated:
The compound interest formula
A = P × (1 + r ÷ n)^(n × t)
A is the final amount, P the starting amount, r the yearly rate as a decimal, n how many times a year interest is added, and t the number of years. Regular deposits are added on top: each one then earns compound interest for the rest of the term.
Example: $10,000 at 5% compounded monthly for 10 years grows to about $16,470. With simple interest it would only reach $15,000. The extra $1,470 is interest earned on interest.
The rule of 72
Divide 72 by the yearly rate to estimate how many years it takes to double your money. At 6%, money doubles in about 12 years; at 9%, about 8 years.
Why starting early matters
Time is the biggest lever. Someone who invests $200 a month from age 25 to 35 and then stops can end up with more at 65 than someone who invests $200 a month from 35 to 65, because the early money compounds for longer.
Illustration only, not financial advice. Real investment returns vary from year to year and can be negative.
Frequently asked questions
What’s the difference between simple and compound interest?
Simple interest is paid only on your original amount. Compound interest is also paid on interest you’ve already earned, so growth speeds up over time.
Does compounding frequency matter much?
A little. Daily compounding earns slightly more than yearly at the same rate, but the rate and the number of years matter far more.
What rate should I use?
Use your savings account’s APY for cash. For long-term stock market estimates, many people use 5–7% after inflation, but returns aren’t guaranteed.
Related tools
Percentage Calculator
X% of Y, percentage change, increase and decrease.
Loan Calculator
Monthly payment, total interest and schedule.
Zakat Calculator
Work out zakat on savings, gold and silver.
Discount Calculator
Sale price, savings and stacked discounts.
Salary to Hourly Calculator
Convert hourly, monthly and yearly pay.
Tip Calculator
Work out the tip and split the bill.