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    Compound Interest Calculator

    See how your starting balance and regular contributions could grow over time. Separate the money you put in from the growth it earns, and explore what inflation changes.

    Calculate your growthHow it works

    Free to use · No account required · Calculations run in your browser

    A simple way to see the bigger pictureChange the example to your own numbers
    Your assumptions

    Start with your numbers

    Use a constant annual rate to explore a scenario.

    The amount you already have.

    How much you add each time.

    A whole number from 0 to 100.

    An assumption, not a forecast.

    Formatting only; no conversion.

    You add $6,000 per year with these contributions.

    Compounding, timing & inflation

    For a quoted APY, select effective.

    How often the nominal rate compounds.

    See purchasing power in today’s money.

    Optional. Clear this checkbox to remove saved inputs.

    Default: monthly compounding, contributions at the end of each month. No taxes, fees, withdrawals or changing rates are modeled. Example rates are illustrative.

    Your projection
    Example

    Estimated future balance

    —

    Calculate to see a projection.

    Total paid in—
    Added contributions—
    Interest / growth—

    Understand your growth

    Three things drive this projection: your starting balance, how much you add, and how long your money compounds.

    What is compound interest?

    Compound interest means earning interest on your original money and on interest already earned. If you leave the growth invested, each period starts from the new balance. Regular deposits give you another way to build that balance.

    Your total paid in is your starting balance plus all new contributions. Interest / growth is the projected final balance minus that total.

    The compound interest formula

    A = P × (1 + r / m)m × t

    For a lump sum, P is the starting amount, r is the nominal annual rate as a decimal, m is compounding periods per year, and t is years. A is the future balance.

    With regular contributions, each deposit compounds for the time it remains invested. This calculator adds those deposits at your selected start or end of each period.

    A simple example: $10,000 at 5%

    With annual compounding and no new deposits, $10,000 becomes $16,288.95 after 10 years. That is $6,288.95 of growth. Add $100 at the end of every month, using an equivalent monthly growth rate, and the projection becomes $31,725.26.

    Hypothetical fixed 5% nominal rate, compounded annually. These are examples, not promised returns.

    Turn the projection into a savings goal

    See when you could reach your first $100k, save a baseline on your device, and track your actual balance over time.

    Open the free $100k Planner →

    Compound interest calculator FAQs

    How do I calculate compound interest with monthly contributions?

    Enter your starting balance, the amount added each month, the annual rate and the years. Select monthly contributions. Under compounding settings, choose the rate type and compounding frequency. The calculator grows the existing balance and adds each deposit at your chosen time.

    Is the contribution amount monthly or per deposit?

    It is the amount of each deposit. A $500 contribution means $6,000 per year when monthly, $13,000 when every two weeks, $26,000 when weekly, or $500 when annual. The line below the inputs shows your annual contribution total.

    What is the difference between a nominal rate and APY?

    A nominal annual rate is split across the selected compounding periods. For example, 5% compounded monthly has an effective annual growth rate of about 5.12%. APY already includes annual compounding effects. If you enter a quoted APY, choose “Effective annual rate / APY” so the calculator does not compound it a second time.

    What happens when deposits and compounding use different frequencies?

    The calculator converts your selected compounding rate to an equivalent rate for each contribution period: i = (1 + r / m)m / c − 1, where c is deposits per year. It then applies that rate between deposits. For APY, i = (1 + r)1 / c − 1. This assumes equivalent growth between dates. A bank’s actual interest accrual, crediting rules and day count may differ.

    Do beginning-of-period contributions make a difference?

    Yes. At a positive rate, a deposit made at the start of the period earns one extra period of growth compared with the same deposit made at the end. The default is end-of-period contributions. At a negative rate, earlier contributions also experience that period’s loss.

    How does the inflation adjustment work?

    The final balance in today’s money equals the projected future balance divided by (1 + annual inflation rate)years. It is a purchasing-power estimate using your constant assumption. Contributions stay fixed in nominal terms; they do not rise with inflation.

    Can I use this for stock market returns or savings accounts?

    You can explore a constant-rate scenario for either. Investment returns fluctuate and can be negative, while account interest rates can change. For an effective annual investment return or a savings account APY, choose the effective rate option. This tool does not model volatility, taxes, fees or withdrawals.

    Can I save or export my results?

    Download a CSV with your calculated assumptions and year-by-year balances. Recalculate after changing inputs to export the updated scenario. “Remember my inputs” stores them in this browser on this device; it does not create an account or sync across devices.

    More from Top Wealth Guide

    Method checked October 9, 2026. Educational projections only; actual results depend on rates, deposit dates, account terms, costs and investment performance.

    Further reading: Investor.gov: compound growthInvestor.gov: compound interest calculator