Introduction
This interest calculator shows you how your money can grow over time through the power of compound interest. Enter your starting amount, add any monthly or yearly contributions, and set your interest rate to see your future balance. The tool breaks down exactly how much of your final balance comes from your initial investment, your deposits, and the interest you earn. You can also adjust for taxes and inflation to get a more realistic picture of your money's true buying power.
Whether you are saving for retirement, a college fund, or any other goal, this calculator helps you plan ahead. It shows results in easy-to-read charts and a detailed schedule so you can track your balance year by year or month by month. Try different numbers to see how small changes in your savings rate or interest rate can make a big difference over time. For a quick estimate of how long it takes your money to double, try our Rule of 72 Calculator.
How to Use Our Interest Calculator
Enter your investment details below to see how your money grows over time. The calculator will show your ending balance, total interest earned, and a breakdown of your savings growth.
Initial Investment – Enter the amount of money you are starting with. This is the lump sum you invest on day one.
Annual Contribution – Enter any extra money you plan to add once per year. Set this to 0 if you do not plan to make yearly deposits.
Monthly Contribution – Enter the amount you plan to add every month. Even small monthly deposits can grow a lot over time.
Contribution Timing – Choose whether your deposits are added at the beginning or end of each period. This affects how much interest your contributions earn.
Annual Interest Rate – Enter the yearly interest rate you expect to earn on your investment. For example, enter 6 for a 6% rate. If you want to compare this to the annual percentage yield that accounts for compounding, use our APY Calculator.
Compounding Frequency – Choose how often your interest is calculated and added to your balance. Common options include monthly, quarterly, and annually. More frequent compounding means slightly more interest earned.
Years – Enter the number of full years you plan to keep your money invested.
Months – Enter any extra months beyond full years. For example, for 5 years and 6 months, enter 5 in Years and 6 in Months.
Tax Rate – Enter the tax rate applied to your interest earnings each period. Leave this at 0 if your account is tax-free. To determine your applicable rate, check out our Effective Tax Rate Calculator.
Inflation Rate – Enter the expected yearly inflation rate. This adjusts your ending balance to show what it would be worth in today's dollars. You can explore historical purchasing power changes with our Inflation Calculator.
Press Calculate to see your results. Press Reset to return all fields to their default values.
What Is Compound Interest?
Compound interest is the interest you earn on both your original money and the interest that has already been added. Think of it like a snowball rolling downhill — it keeps getting bigger because new snow sticks to the snow already there. If you put $1,000 in an account that pays 5% interest per year, you earn $50 the first year. The next year, you earn interest on $1,050 instead of just $1,000. Over time, this effect grows faster and faster. Our dedicated Compound Interest Calculator lets you dive deeper into this concept with additional options. If you only need to calculate interest without compounding, our Simple Interest Calculator is a useful alternative.
How This Calculator Works
This interest calculator shows you how your money can grow over time. You enter your starting amount, any extra money you plan to add each month or year, the interest rate, and how long you plan to save. The calculator then does the math and shows you your total ending balance, how much of that is interest, and how much came from money you put in yourself. If you want to project the total future worth of your savings and contributions, our Future Value Calculator is another helpful tool. You can also use our Investment Calculator or Savings Calculator for broader planning scenarios.
Key Terms to Know
Principal is the money you start with. Contributions are extra deposits you add over time. The interest rate is the percentage your money earns each year. Compounding frequency is how often interest gets calculated and added to your balance — monthly, daily, or even continuously. The more often interest compounds, the more you earn. To understand the difference between a stated rate and an effective rate, compare results using our APR Calculator and APY Calculator.
Why Tax and Inflation Matter
Taxes reduce how much interest you actually keep. If your interest gets taxed, your money grows slower. Inflation is the rise in prices over time. Even if your account balance goes up, your money may buy less in the future. This calculator lets you enter both a tax rate and an inflation rate so you can see a more realistic picture of your savings. To understand how inflation erodes purchasing power over specific periods, visit our Inflation Calculator. If you are saving in a tax-advantaged account like a certificate of deposit, our CD Calculator can give you a more tailored projection. For tax-sheltered retirement accounts, explore our 401k Calculator or Roth IRA Calculator.
Contribution Timing: Beginning vs. End
You can choose whether your deposits are added at the beginning or end of each period. Adding money at the beginning means it earns interest for that whole period, so your balance ends up slightly higher. This small difference adds up over many years. If you are exploring structured periodic payments like annuities, our Annuity Calculator handles beginning-and-end-of-period timing in the context of regular payout or accumulation plans. For long-term retirement planning where contribution timing and growth are critical, try our Retirement Calculator or Coast FIRE Calculator.