Estimate how your investments could grow over time with compound interest.
This compound interest calculator estimates how your money can grow over time based on four inputs: your starting balance, monthly contributions, annual interest rate, and investment period. It uses the standard compound interest formula and calculates returns monthly to give you a practical long-term projection.
Compound interest is one of the most important ideas in personal finance. Unlike simple interest, which is calculated only on your original investment, compound interest builds on your growing balance. Every time interest is earned, it is added back into your principal, and the next round of interest is calculated on that larger amount.
According to Investor.gov, the U.S. Securities and Exchange Commission’s investor education portal, compound interest is one of the most important concepts for investors to understand.
To show how this calculator works, consider the following example. The figures update when you change the currency at the top of the calculator.
Your total out-of-pocket contributions over 20 years would be around , yet the portfolio could grow to more than . The difference comes from compound growth.
The larger your starting balance, the more money you have working for you from day one. Even a small starting amount can become meaningful when it has enough time to compound.
Regular contributions often have a major impact on your final balance. Automating monthly investments can keep your plan consistent even when markets move up or down.
Higher returns can increase long-term growth, but they also tend to involve higher risk. Many long-term investors use diversified funds to pursue steady growth over time.
Time is often the most powerful factor in compound interest. The longer your money stays invested, the more opportunity it has to grow.
The table below shows how a one-time investment of grows at three different annual returns with no additional contributions.
| Years Invested | at 6% | at 8% | at 10% |
|---|
Adding regular monthly contributions on top of a lump-sum starting investment can increase these values substantially.
Every year you wait reduces the time your money has to compound.
Monthly investing helps you stay disciplined and keeps your money working.
Reinvesting earnings allows the compounding cycle to continue.
Lower fees leave more of your money invested for long-term growth.
Long-term investors often benefit from staying invested rather than trying to time the market.
Compound interest is interest earned on both your original investment and on interest that has already been added to your balance.
More frequent compounding can lead to slightly higher returns because interest is added and reinvested more often.
No. Investment returns are not guaranteed. Savings accounts may provide fixed interest, but market investments can rise or fall.
Savings accounts, CDs, index funds, ETFs, mutual funds, dividend reinvestment plans, and retirement accounts can all benefit from compounding.
Start early, contribute regularly, reinvest earnings, reduce fees, and keep a long-term investment plan.
Many long-term planning examples use 6% to 8% as a conservative estimate, but actual returns vary and are never guaranteed.
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Disclaimer: This calculator is provided for educational and informational purposes only. Results are estimates based on the inputs you provide and a fixed annual rate. Actual investment returns vary and are not guaranteed. This is not financial advice. Always consult a qualified financial professional before making investment decisions. See our full Disclaimer and Privacy Policy.