Free Investment Growth Calculator
Compound Interest Calculator
Calculate how an initial investment and recurring monthly contributions could grow with compound interest. Estimate future value, total contributions, and interest earned based on your expected annual return and investment period.
Enter your investment details
Estimate how your money may grow over time with compound interest and recurring monthly contributions.
Growth Results
Enter your investment details
Your estimated future value and compound interest results will appear here.
How to use this compound interest calculator
Enter your starting investment, expected annual rate of return, investment period, and any recurring monthly contribution. The calculator estimates how much the account could grow over time based on the assumptions you provide.
You can change the contribution amount, rate of return, or time period to compare different saving and investing scenarios.
Future Value
The estimated total account value at the end of the selected investment period.
Total Contributions
The total amount you personally contributed, including the initial investment and recurring deposits.
Interest Earned
The estimated growth above the amount you personally contributed.
How compound interest works
Compound interest means that growth can be earned not only on your original principal but also on previously accumulated interest or investment returns.
Over longer periods, this compounding effect can significantly increase the estimated future value of money. Regular contributions can further increase the amount available to compound.
Compound interest formula
A = P(1 + r/n)ⁿᵗ
A = future value
P = initial principal
r = annual interest rate
n = number of compounding periods per year
t = number of years
When recurring contributions are included, each contribution has a different amount of time to compound, so additional calculations are required.
Compound interest calculation example
Suppose you start with $10,000, contribute $500 each month, and assume an average annual return of 7% over 20 years.
Initial investment: $10,000
Monthly contribution: $500
Annual return: 7%
Investment period: 20 years
The calculator estimates the future value by combining your original investment, all recurring contributions, and the hypothetical compound growth generated over the investment period.
How monthly contributions affect compound growth
Regular monthly contributions can have a substantial impact on long-term investment growth because each new contribution adds more principal that may earn future returns.
Contributions made earlier generally have more time to compound than contributions made later. Increasing either the amount contributed or the length of time invested can significantly affect the estimated future value.
Why time matters with compound interest
Time is one of the most important variables in compound growth. The longer money remains invested, the more opportunities there are for previously earned returns to generate additional returns.
For example, the same investment earning the same hypothetical annual return for 30 years has significantly more time to compound than an investment held for only 5 or 10 years.
Investment returns are not guaranteed
Real investments do not normally earn the same return every year. Market values can rise or fall, and fees, taxes, inflation, volatility, and investment losses can materially affect actual results.
Monthly vs. quarterly vs. annual compounding
Compounding frequency describes how often earned interest is added to the account balance. When all other assumptions are equal, more frequent compounding can produce a slightly higher future value because accumulated interest begins earning additional interest sooner.
Monthly
12 times per year
Interest is compounded once each month.
Quarterly
4 times per year
Interest is compounded once every three months.
Annually
1 time per year
Interest is compounded once per year.
Simple interest vs. compound interest
Simple interest is generally calculated only on the original principal. Compound interest can be calculated on both the original principal and previously accumulated interest.
Simple Interest
Interest is based primarily on the original principal, so previously earned interest does not itself generate additional interest.
Compound Interest
Previously accumulated interest can become part of the balance used to calculate future interest.
How the rate of return affects future value
Even relatively small differences in an assumed annual return can produce significantly different long-term estimates because those differences can also compound over time.
When using an investment calculator, it can be helpful to test several return assumptions rather than relying on a single forecast.
Does compound interest account for inflation?
Standard compound interest calculations usually show nominal future value and do not automatically adjust for inflation. Inflation can reduce the purchasing power of money over time, meaning a future account balance may buy less than the same dollar amount would today.
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What is compound interest?
Compound interest is interest calculated on both the original principal and previously accumulated interest. This can allow money to grow at an increasing rate over time.
How do I calculate compound interest?
A common compound interest formula is A = P(1 + r/n)ⁿᵗ, where P is the initial principal, r is the annual interest rate, n is the number of compounding periods per year, and t is the number of years.
What is the difference between simple and compound interest?
Simple interest is generally calculated only on the original principal. Compound interest can also generate growth on previously accumulated interest.
How do monthly contributions affect compound growth?
Regular contributions increase the amount available to potentially earn future returns. Contributions made earlier generally have more time to compound than contributions made later.
Is monthly compounding better than annual compounding?
When the stated annual rate and other assumptions are the same, more frequent compounding can produce a slightly higher future value. The size of the difference depends on the rate and investment period.
How long does it take money to double?
The time required depends on the rate of return and compounding frequency. Higher returns generally reduce the estimated time required for an investment to double, but actual investment returns are not guaranteed.
Does this calculator include monthly contributions?
Yes. You can enter a recurring monthly contribution in addition to your starting investment to estimate how regular deposits may affect future value.
Does compound interest account for inflation?
Not automatically. Standard compound interest calculations typically show nominal values unless inflation is separately incorporated into the assumptions.
Does this calculator predict actual investment returns?
No. The calculator provides hypothetical estimates using the rate you enter. Actual investment returns fluctuate and may be higher, lower, or negative.
This compound interest calculator is provided for general informational and educational purposes only. Results are hypothetical estimates and do not represent guaranteed investment performance. Taxes, fees, inflation, market volatility, contribution timing, and other factors may materially affect actual results.