Investment Growth Calculator
Enter your initial investment, monthly contributions, and expected return rate to project your portfolio value over any time horizon. See exactly how much comes from compound growth versus your own contributions — and watch the compounding effect accelerate over time.
Adjust the inputs to model any investment scenario — results update instantly:
Initial investment
The lump sum you invest today. This is your starting principal — even a small amount has a dramatic impact over long periods because it compounds from day one. Enter 0 if you are starting with no savings and plan to build through regular contributions.
Monthly contribution
How much you plan to add each month. Regular contributions are the most powerful tool for building wealth over time. A consistent $500/month invested for 30 years at 7% grows to over $566,000 from contributions alone — plus compounding on top.
Annual return rate
The expected average annual return on your investments. A diversified stock market index fund has historically returned 7–10% nominally. Use 5–7% for conservative real-return estimates. Adjust the slider to see how sensitive your results are to return assumptions.
Time horizon
The number of years you plan to invest. Time is the most powerful variable in this calculator — doubling the investment period more than doubles the final value due to compounding. Model your actual expected investment period, not an idealized one.
Compound frequency
Monthly compounding means returns are applied each month, producing slightly higher final values than annual compounding. For most brokerage accounts and index funds, monthly compounding is the realistic assumption. The difference grows over very long periods.
Final Portfolio Value
The total value of your investment at the end of the selected time horizon, including all contributions and compound growth. This is the number to use when setting savings targets or modeling retirement scenarios.
Total Contributed
The total amount you personally invested: your initial lump sum plus all monthly contributions added over the entire period. This is your 'break-even' — you never lost money if the final value exceeds this.
Total Growth
The profit generated purely by compounding — the difference between your final portfolio value and what you actually put in. This grows dramatically in the later years of the investment period due to the exponential nature of compound interest.
Growth Multiplier
How many times your money grew relative to what you contributed. A 3× multiplier means for every $1 you invested, your portfolio returned $3. This metric makes it easy to compare scenarios with different time horizons and return rates.
Year-by-Year Table
The breakdown table shows your balance, total contributed, and total growth at each year (or every 5 years for longer periods). Use it to identify the inflection point where compound growth starts outpacing your own contributions.
The calculator uses the standard future value formula, which accounts for both a lump sum initial investment and regular periodic contributions. Two compounding modes are available: monthly (most common for brokerage accounts) and annual.
FV = P × (1 + r)ⁿ + C × ((1 + r)ⁿ − 1) / r
P = initial investment · r = monthly rate · n = total months · C = monthly contribution
For monthly compounding: r = annual rate ÷ 12, n = years × 12. For annual compounding, contributions are treated as a single annual lump sum and the formula uses the annual rate directly.
Total Interest = Final Value − Total Contributed
Total Contributed = Initial Investment + (Monthly Contribution × 12 × Years)
The year-by-year table applies the same formula at each yearly interval to give you the full trajectory — not just the final number. When the rate is zero, the formula simplifies to: Final Value = Initial Investment + Monthly Contribution × 12 × Years.
Why compounding accelerates over time
In early years, growth is modest because the base is small. By year 20, you are earning returns on returns accumulated over two decades. The chart shows this clearly — the growth area gets proportionally larger each year.
Monthly vs. annual compounding
Monthly compounding applies returns 12 times per year rather than once. Over long periods this compounds to a meaningful difference. At 7% over 30 years on $100K, monthly compounding produces roughly $20K more than annual.
Return rate sensitivity
Small changes in the assumed return rate produce large differences over long periods. The difference between 6% and 8% over 30 years on a $500/month investment is over $200,000. This is why keeping investment costs low (expense ratios, fees) matters enormously.
The contribution sweet spot
Contributions matter most in the early years when the portfolio is small. As the portfolio grows, compound growth on the existing balance progressively outpaces new contributions. After 20–25 years, stopping contributions entirely still produces impressive results.
The consistent saver — 20 years
Long-term index investor — 30 years
Lump sum only — 40 years
The lump sum example shows compounding at its most powerful: $50,000 invested without a single additional dollar becomes $748,000 over 40 years. Time and return rate are the primary drivers — not the size of your monthly contribution. Starting early is worth more than contributing more later.
Albert Einstein is often (perhaps apocryphal) credited with calling compound interest the eighth wonder of the world. Whether or not he said it, the math is unambiguous: compound interest is the mechanism by which modest, consistent saving transforms into life-changing wealth.
The key insight: you earn returns not just on your contributions, but on every dollar of return you have ever earned. A 7% return in year 25 is earned on a portfolio that includes 24 years of compounded growth — not just your original deposits.
This is why early investing is so valuable. A 25-year-old who invests $5,000 once and never touches it will likely have more money at 65 than a 35-year-old who invests $5,000 every year for 30 years — because the 25-year-old's money gets an extra 10 years of compounding.
For FIRE planning, this insight reinforces the core strategy: maximize your investment rate early, choose low-cost diversified index funds, and let time do the heavy lifting. See our index fund investing guide for how to structure your investments.
The Rule of 72
A quick mental shortcut: divide 72 by your annual return rate to estimate how many years it takes to double your money. At 7%, money doubles roughly every 10 years (72 ÷ 7 = 10.3). At 10%, every 7.2 years.
Why fees destroy returns
A 1% annual fee on a $500,000 portfolio costs $5,000 per year — but the real cost is the compounding you lose. Over 20 years, that 1% fee could consume over $250,000 in compounded growth. Always check expense ratios.
Time beats contribution size
Delaying investing by 5 years can cost more than doubling your monthly contribution afterward. Use this calculator to model the cost of waiting — the numbers are sobering and motivating.
Sequence of returns matters
This calculator assumes a constant return rate, which is a simplification. In reality, returns vary year-to-year. Early strong returns produce better outcomes than the same average return with poor early years — especially important near retirement.
A 7% nominal return is a reasonable baseline for a diversified stock market portfolio, based on long-run historical averages. For inflation-adjusted (real) returns, 4–5% is more appropriate. Use a lower rate (5–6%) for conservative planning and a higher rate (8–10%) to model optimistic scenarios. The safest approach is to run multiple scenarios and understand the range of outcomes.
No — this calculator uses nominal (not inflation-adjusted) returns. If you enter a 7% return and inflation is 3%, your real purchasing power grows at roughly 4% per year. To model real returns, simply reduce your assumed return rate by your expected inflation rate. For example, enter 4% instead of 7% to model a 3% inflation environment.
Monthly compounding applies your annual return rate in smaller increments each month, which means you earn returns on earlier returns sooner. Over long periods this produces slightly higher final values. Most brokerage accounts and mutual funds compound continuously or daily in practice — monthly compounding is a close approximation. The difference is small but grows over decades.
This calculator provides accurate mathematical projections based on the inputs you provide. The key limitation is that real-world returns are not constant — they fluctuate year-to-year. The calculator assumes your assumed return rate every single year, which won't happen in practice. Use the results as a planning guide, not a guarantee. Conservative return assumptions give more realistic outcomes.
Yes — include the current value of all invested accounts: 401(k), IRA, Roth IRA, and taxable brokerage accounts. Your monthly contributions should include all sources of regular investing (payroll deductions plus manual contributions). The calculator models total portfolio growth regardless of which account type holds the money.
Set your time horizon to the point when you stop contributing, note the final value, then run the calculator again with that value as the initial investment, zero monthly contributions, and the remaining time horizon. This two-step approach models a period of active saving followed by passive compounding.
Your FIRE number is the portfolio target — typically 25× your annual expenses. This calculator helps you project whether your current savings rate and timeline will reach that target. For a complete FIRE projection with income, expenses, and retirement age, use the FIRE Calculator.
No — and this is the most important caveat to any investment projection. Historical averages (like the 7% S&P 500 figure) are useful planning guides, but they include periods of severe drawdown (2000–2002, 2008–2009, 2020) that this calculator smooths over. Future returns may be higher or lower. Diversify, keep costs low, and plan for a range of scenarios.
Calculate your full FIRE timeline
See your complete path to financial independence — combining your investment growth projection with your expenses and FIRE number in one place.
Find your FIRE Number
Calculate exactly how much you need to retire based on your annual expenses and withdrawal rate — your investment growth target.
Optimize your savings rate
Discover how dramatically increasing your savings rate compresses your path to financial independence.
Disclaimer: This calculator is for educational and informational purposes only. It does not constitute financial, investment, or tax advice. All projections are estimates based on the assumptions you enter — actual investment returns vary significantly from year to year and past performance does not guarantee future results. This calculator assumes a constant annual return rate, which does not reflect real-world market volatility. Consult a qualified financial advisor before making investment decisions.