Enter your initial investment, monthly contribution, annual interest rate, and time period to see how your money grows with compound growth. The Compound Growth Calculator returns your future value, total contributions, and total interest earned — broken down visually so you can see exactly what compounding does over time.
Future Value
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Total Contributions
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Total Interest Earned
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Growth Multiple
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Compound interest is the interest you earn on both your original principal and the accumulated interest from previous periods. Unlike simple interest, which only grows on the initial amount, compound growth accelerates over time — meaning your money grows faster the longer it stays invested.
The standard formula is A = P(1 + r/n)^(nt) + contributions, where A is the final amount, P is the principal, r is the annual interest rate (as a decimal), n is the number of compounding periods per year, and t is the number of years. Regular contributions are added using a future value of annuity formula on top of the lump sum calculation.
The more frequently interest compounds, the more you earn. Daily compounding produces slightly more than monthly, which produces more than annually. For most long-term investments, the difference between monthly and daily compounding is small, but over decades it can add up meaningfully.
Yes — significantly. Regular monthly contributions amplify the compounding effect because each new deposit starts earning interest immediately. Even a modest monthly contribution of $100–$500 can add tens of thousands of dollars to your final balance over a 20–30 year horizon compared to a lump-sum-only approach.
Historical stock market averages for broad index funds have ranged from 7–10% annually before inflation. For savings accounts and CDs, rates are typically 1–5% depending on the economic environment. Use a conservative estimate (5–7%) for long-term projections to avoid overstating your results.
The Rule of 72 is a quick mental shortcut: divide 72 by your annual interest rate to estimate how many years it takes to double your money. For example, at a 7% return, your investment doubles roughly every 10 years (72 ÷ 7 ≈ 10.3 years). It works best for interest rates between 4% and 12%.
This calculator is a great starting point for retirement planning — you can model different contribution levels, time horizons, and expected returns. However, it does not account for taxes, inflation, or fees. For a full retirement plan, consult a licensed financial advisor who can factor in your complete financial picture.
Start as early as possible to give time its full effect, contribute consistently each month, reinvest all returns rather than withdrawing them, and minimize fees on your investments. Even a 1% reduction in annual fees can translate into tens of thousands of dollars more at retirement due to the compounding impact.