Compound Interest Calculator
Enter your numbers below. The calculator updates the estimate using the assumptions you provide.
This calculator is an estimate. Actual savings and investment results depend on the financial product, rate, fees, contributions, taxes and market performance. Investment returns are not guaranteed.
What Is Compound Interest?
Compound interest is interest calculated on an initial amount plus interest that has already accumulated. In simple terms, your money can earn returns, and those accumulated returns can become part of the balance used to calculate future returns.
The effect becomes more noticeable over longer periods because growth can build on previous growth. Regular contributions can increase the amount available to compound as well.
Compound Interest Formula
For a single initial amount compounded at a fixed rate, the standard compound interest formula is:
Where:
| Symbol | Meaning |
|---|---|
| A | Future value of the account or investment |
| P | Initial principal or starting amount |
| r | Annual interest rate expressed as a decimal |
| n | Number of compounding periods per year |
| t | Number of years |
The PaycheckMint calculator also accounts for recurring monthly contributions, which require an additional contribution-growth calculation.
How the Compound Interest Calculator Works
The PaycheckMint calculator combines your starting amount, recurring contributions, assumed annual rate, investment period and compounding frequency to estimate a future balance.
This is the amount you already have available at the beginning of the calculation.
Enter how much you expect to add each month. Contributions can significantly affect long-term growth.
Longer periods give assumed returns and contributions more time to compound.
Use an annual rate appropriate for the type of account or investment you are modeling.
Choose annually, semiannually, quarterly, monthly or daily depending on the product being modeled.
What Is Compounding Frequency?
Compounding frequency describes how often interest is added to the balance during a year. Common frequencies include annual, semiannual, quarterly, monthly and daily compounding.
| Frequency | Times per year | Example |
|---|---|---|
| Annually | 1 | Interest compounds once per year. |
| Semiannually | 2 | Interest compounds twice per year. |
| Quarterly | 4 | Interest compounds four times per year. |
| Monthly | 12 | Interest compounds twelve times per year. |
| Daily | 365 | Interest compounds approximately every day. |
The actual terms of a bank account, savings product or investment determine how interest or returns are calculated. Check the account or investment documentation when you need an exact calculation.
Compound Interest vs. Simple Interest
The key difference is what happens to previously earned interest. With simple interest, interest is calculated only on the original principal. With compound interest, previously accumulated interest can also earn interest.
| Simple Interest | Compound Interest | |
|---|---|---|
| Interest calculated on | Original principal | Principal plus accumulated interest |
| Effect over time | Generally more linear | Can accelerate as the balance grows |
| Common use | Certain loans and financial calculations | Many savings and investment growth calculations |
Compound Interest Example
Suppose you start with $5,000, contribute $250 per month, and use an assumed annual return of 7% for a period of 20 years.
The final result depends on the compounding and contribution assumptions. The important point is that both the starting balance and ongoing contributions have time to grow.
Use the calculator above to change the assumptions and see how the estimated result changes.
How Monthly Contributions Affect Compound Growth
A starting balance is not the only factor that matters. Regular contributions can add substantially to the amount invested over a long period.
For example, someone who contributes $300 every month for 20 years contributes $72,000 from those monthly deposits alone, before considering any investment growth.
If those contributions remain invested, each contribution has its own opportunity to earn returns. Earlier contributions have more time to compound than later contributions.
Why Time Matters With Compound Interest
Time gives a balance more opportunities to earn returns and for those returns to become part of the balance. This is why long-term calculations can look very different from short-term calculations even when the assumed annual rate stays the same.
Starting earlier can also give recurring contributions more time to grow. However, a longer investment period does not guarantee a positive investment result because actual returns can fluctuate.
Compound Interest and Investing
People often use the term "compound interest" when discussing investing, but investment returns are not the same as a guaranteed bank interest rate.
A stock, ETF, mutual fund or other investment can increase or decrease in value. Dividends or other distributions may also be reinvested. When returns remain invested, the general concept of compounding can apply.
For investment planning, use the calculator's rate as an assumption, not as a promise of what an investment will earn.
Explore the PaycheckMint Investing Guide →Compound Interest for Savings
Compound interest can also apply to savings products when the account pays interest and that interest is added to the balance.
For savings accounts, the rate and account terms can change. If you are calculating the future value of a specific savings account, use the rate and compounding information provided by the financial institution.
The calculator is useful for planning scenarios, but it should not be treated as an exact forecast of what a particular bank account or investment will produce.
What Interest Rate Should You Use?
There is no single rate that should be used for every calculation. The appropriate assumption depends on what you are modeling.
For a savings account, you can use the account's stated rate when estimating its growth. For investments, future returns are uncertain, so using multiple scenarios can be more informative than relying on a single assumed rate.
Try changing the calculator's annual rate to see how sensitive the projected result is to your assumption.
What Can You Use a Compound Interest Calculator For?
Common Compound Interest Calculation Mistakes
Using a guaranteed return for an investment
Investment returns are uncertain. An assumed rate in a calculator is only a mathematical scenario.
Forgetting recurring contributions
If you regularly add money to an account, excluding those contributions can make your calculation substantially different from your actual plan.
Ignoring fees and taxes
A basic compound interest calculation does not automatically account for investment fees, taxes or inflation. These factors can affect your actual outcome.
Assuming the same rate every year
A fixed rate is convenient for a calculator, but real investment returns can vary from year to year.
Compound Interest Calculator FAQs
What is compound interest?
Compound interest is interest earned on an initial amount plus previously accumulated interest. Over time, this can allow growth to build on earlier growth.
How does a compound interest calculator work?
It uses inputs such as the starting amount, recurring contributions, annual rate, investment period and compounding frequency to estimate a future balance.
What is the compound interest formula?
For a single principal amount, the standard formula is A = P × (1 + r ÷ n)nt. The PaycheckMint calculator also accounts for recurring monthly contributions.
How often can interest compound?
Common compounding frequencies include annually, semiannually, quarterly, monthly and daily. The actual frequency depends on the financial product.
Does monthly investing compound?
Regular contributions can increase the amount of money available to earn future returns. Each contribution has its own period of time to potentially grow.
Is compound interest guaranteed?
No. A calculator using a fixed rate produces a mathematical estimate. Actual investment returns can vary and can be negative.
Can I use this calculator for a savings account?
Yes. You can use it for planning a savings scenario, but use the actual rate and compounding terms provided by your financial institution when you need a product-specific calculation.
Does the calculator account for inflation?
No. The displayed future value is a nominal estimate and does not automatically account for inflation. The future purchasing power of that amount may be lower than its nominal value.
Does the calculator include investment fees?
No. This basic calculator does not subtract investment management fees, account fees or other costs.
Compound Interest Calculator Disclaimer
PaycheckMint's compound interest calculator is provided for general educational and planning purposes. Results are estimates based on the assumptions entered and are not a guarantee of future savings or investment performance. Actual results can differ because of changing rates, investment returns, contributions, fees, taxes, inflation and other factors. PaycheckMint does not provide individualized investment, financial, tax or legal advice.