Compound Interest Calculator
Calculate how your money could grow over time with compound interest, regular contributions, and an estimated annual rate of return.
Calculate Compound Interest
Enter your starting investment, regular contributions, interest rate, investment period, and compounding frequency to estimate your future balance.
Starting Investment
Regular Contributions
Interest & Growth
Investment Period
Inflation Adjustment
Compound Interest Result
Estimated future value of your investment, including regular contributions.
| Initial Investment | — |
| Regular Contribution | — |
| Contribution Frequency | — |
| Annual Interest Rate | — |
| Compounding Frequency | — |
| Investment Period | — |
| Total Contributions | — |
| Total Interest Earned | — |
| Inflation-Adjusted Value | — |
Step-by-Step Calculation
What Is Compound Interest?
Compound interest is interest earned on both the original amount of money and previously accumulated interest. Over longer periods, compounding can have a significant effect on the growth of savings and investments.
Compound Interest Formula
For a single initial investment without additional contributions, the standard compound interest formula is:
A = future value
P = initial principal
r = annual interest rate as a decimal
n = number of compounding periods per year
t = time in years
When regular contributions are added, the future value of those contributions is calculated separately and combined with the growth of the initial investment.
Why Compounding Frequency Matters
Interest can be compounded daily, weekly, monthly, quarterly, semiannually, or annually. When other assumptions remain the same, more frequent compounding generally results in a slightly higher effective return.
Why Regular Contributions Matter
Adding money regularly can substantially increase the amount accumulated over time. Each contribution gets an opportunity to earn returns for the remaining investment period.
Compound Interest Example
Suppose you invest 10,000 initially and earn an average annual return of 7% for 20 years, while also adding 500 each month. The calculator combines the initial investment and regular contributions to estimate the potential future value.
The actual outcome can differ because investment returns are not guaranteed and may vary from year to year.
Inflation and Purchasing Power
A future balance may have less purchasing power than the same amount today because prices can increase over time. The inflation adjustment provides an estimate of what the projected balance could be worth in today’s money.
Related Calculators
How to Use This Compound Interest Calculator
- Choose the currency you want to display.
- Enter your initial investment and, if applicable, a regular contribution.
- Select how often you contribute and how often interest is compounded.
- Enter the assumed annual interest rate and investment period.
- Optionally enter an expected inflation rate to estimate purchasing power in today’s money.
- Select Calculate Compound Interest to review the estimate and step-by-step calculation.
Compound Interest vs. Simple Interest
Simple interest is calculated only on the original principal, while compound interest allows previously earned interest to become part of the amount that can earn further interest. The difference can become more noticeable as the investment period and compounding frequency increase.
Regular contributions add another layer: money invested earlier has more time to compound than money added near the end of the investment period. This is why contribution timing can materially affect the projected balance.
What This Calculator Assumes
- The annual rate entered by the user remains constant throughout the selected period.
- Interest is compounded at the selected frequency.
- Regular contributions are made at the selected frequency and are modeled consistently throughout the period.
- Inflation is applied as a constant annual rate when an inflation assumption is entered.
- Taxes, investment fees, transaction costs, and changes in contribution amounts are not separately modeled.
Understanding the Results
Future Value is the projected ending balance under the assumptions entered. Total Contributions shows the principal plus regular amounts you contributed. Interest Earned is the projected future value less total contributions. Value in Today’s Money discounts the projected balance using the inflation rate entered.
These figures are useful for comparing scenarios, such as changing the contribution amount, investment period, assumed return, or compounding frequency. They should be treated as estimates rather than promises of future performance.
Worked Example
Consider an initial investment of 10,000 with 500 added each month, a 7% annual rate, monthly compounding, and a 20-year period. The calculator separates the growth of the initial investment from the growth of regular contributions, then combines them to estimate the ending balance.
Changing just one assumption can produce a different result. For example, increasing the monthly contribution or extending the investment period can have a substantial effect because additional money has more time to participate in compounding.
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on the principal and on interest accumulated previously.
Does compounding more frequently always produce a higher result?
When the nominal rate and other assumptions are held constant, more frequent compounding generally produces a slightly higher effective return.
Can I include monthly investments?
Yes. Enter a contribution amount and choose the contribution frequency, such as monthly, weekly, biweekly, quarterly, or annually.
What does the inflation-adjusted value mean?
It estimates the purchasing power of the projected future balance in today’s money using the inflation rate you enter.
Are the results guaranteed?
No. The result is a mathematical projection based on constant assumptions. Actual investment returns can vary and may be affected by fees, taxes, market conditions, and other factors.
What is the difference between interest earned and total contributions?
Total contributions are the amounts you put into the investment. Interest earned is the projected future value minus those contributions.
Important: This calculator is provided for general informational and educational purposes only and does not constitute financial, tax, legal, investment, or other professional advice. Results are estimates based on assumptions entered by the user and are not a guarantee of future investment performance. Actual interest rates, returns, fees, taxes, contributions, inflation, and market conditions may differ substantially. Consider your individual circumstances and consult a qualified professional when appropriate before making important financial decisions.