How to use this calculator
Enter the amount you have invested today, the amount you plan to add each month, your expected annual rate of return and the number of years you plan to invest. The calculator shows the future value of your money, how much of it came from your own contributions and how much came from growth.
Try a few scenarios. Change the monthly contribution or the number of years and watch how the result moves. Time is usually the input with the biggest effect.
What is compound interest?
Compound interest is growth on top of growth. Each year your investment earns a return, and the next year that return earns a return too. Over long periods, the growth on past growth can become larger than the money you put in.
For example, $10,000 that grows at 7% a year becomes about $19,700 after 10 years, about $38,700 after 20 years and about $76,100 after 30 years. You add nothing after the first deposit. The last 10 years add more than the first 20 years together.
The Rule of 72
A quick way to estimate growth is the Rule of 72. Divide 72 by your annual rate of return to get the approximate number of years it takes your money to double. At 6%, money doubles in about 12 years. At 9%, it doubles in about 8 years.
What changes the result most
Three levers drive compound growth:
- Time: starting 10 years earlier often matters more than a higher contribution later.
- Rate of return: small differences add up. Fees reduce your real rate of return every year.
- Regular contributions: steady monthly additions give each new dollar its own time to compound.
Frequently asked questions
What rate of return should I use?
Use a conservative number. Many people test a range, for example 4% to 7% for a diversified portfolio, and look at the result after inflation. Past returns do not guarantee future results.
Does the calculator include taxes and inflation?
No. The result is a before-tax, nominal amount. Money in a Roth IRA can grow tax-free, while a taxable account pays tax on dividends and gains. Inflation reduces what the future amount can buy.
Is compound interest the same as compound growth on stocks?
Not exactly. Savings accounts and bonds pay interest. Stocks grow through price changes and reinvested dividends, and their returns change from year to year. The calculator uses a steady average rate to show the long-term effect.
Keep reading
- Why investing builds more long-term wealth than saving
- How to build wealth in your 30s
- Learning Center: retirement accounts
- Roth conversion calculator
- All free calculators
This calculator gives estimates for education only. It is not personalized financial, tax or legal advice. Check your numbers with a qualified professional before you make a decision.