Formulas and 2026 figures checked & updated: July 2026
Investment Details
Projected Results
Final Portfolio Value
$343,778
How to Use the Investment Return Calculator
- Enter your starting investment — the lump sum you're investing today, or $0 if you're starting from scratch.
- Enter how much you'll contribute each month going forward.
- Set your expected annual rate of return based on your portfolio's asset allocation.
- Enter the number of years you plan to stay invested before you'll need the money.
- Enter an inflation rate and toggle inflation-adjusted if you want the result expressed in today's purchasing power.
- Read your projected balance, contributions versus growth, and the Rule of 72 doubling time. Example: $10,000 to start plus $500/month for 20 years at 7% grows to roughly $300,000 — about $170,000 of that is investment growth, not contributions.
What This Calculator Does
The Investment Return Calculator projects how a brokerage portfolio grows over time, combining an initial lump-sum investment with regular monthly contributions and a compounding annual return. It's built for long-term planning — retirement, a house down payment, or general wealth building outside of tax-advantaged accounts.
Five inputs drive the projection: your initial investment, monthly contribution, expected annual rate of return, investment period in years, and an inflation rate for the real-return view. As a benchmark, the S&P 500 has returned roughly 10% annually before inflation over the long run (about 7% after inflation), while a diversified 60/40 stock-and-bond portfolio has historically returned closer to 6%–7% nominal. The underlying math is also known as the compound annual growth rate (CAGR) model when used to work backward from a starting and ending value, and it's the same formula investors use to estimate how tax-advantaged accounts like a 401(k) or IRA might grow over time.
Use this calculator to check whether your current savings rate is on pace for retirement or another long-term goal, to compare the long-run impact of a higher versus lower expected return or monthly contribution, or to see how sensitive a projection is to inflation before relying on a big future number. Toggle 'inflation-adjusted' to see results in today's purchasing power — a portfolio that grows to $500,000 in 20 years feels very different once inflation is factored in. It's also useful alongside a target withdrawal rate, since many retirement plans use roughly a 4% initial withdrawal rate as a starting point to translate a projected portfolio value into an estimate of sustainable annual income. Running the numbers at a few different assumed return rates side by side is a simple way to stress-test a plan before committing to it.
Formula
FV = PV(1+r)^n + PMT × [((1+r)^n − 1) / r]Future value combines growth on your initial investment with growth on a stream of monthly contributions, both compounding monthly. For the inflation-adjusted view, the same formula is run using a real rate of return (nominal rate minus inflation).
- PVInitial investment (lump sum)
- PMTMonthly contribution amount
- rMonthly rate of return (annual return ÷ 12, nominal or real)
- nTotal number of months invested
Examples
Example 1: $10,000 start, $500/month for 20 years at 8%
Initial investment of $10,000 plus $500/month for 20 years (240 months) at an 8% nominal annual return.
Final portfolio ≈ $323,000 — about $130,000 contributed and $193,000 from investment growth (roughly a 2.5× growth multiple).
Example 2: Same scenario, inflation-adjusted at 3%
Same $10,000 + $500/month for 20 years, but using a real return of 8% − 3% = 5% to reflect today's purchasing power.
Inflation-adjusted value ≈ $209,000 — roughly $114,000 less than the nominal figure, showing why real returns matter for long-term goals.
Example 3: The Rule of 72 in action
A $50,000 investment with no further contributions, growing at 8% per year, with no withdrawals.
Using the Rule of 72 (72 ÷ 8 = 9), the investment roughly doubles to $100,000 in about 9 years and doubles again to $200,000 by year 18.
Key Terms Explained
- Compound Interest
- Interest earned on both your original balance and previously earned interest, so growth accelerates the longer money stays invested.
- Real Return
- An investment's return after subtracting inflation — what your money actually gains in purchasing power.
- Inflation
- The gradual rise in prices that erodes purchasing power, so a dollar buys less over time.
- Principal
- The original amount borrowed or invested, before interest. Each loan payment is split between paying down principal and paying interest.
- Safe Withdrawal Rate
- The share of a portfolio you can withdraw each year with low risk of running out — traditionally around 4% (the “4% rule”).
Continue Your Financial Planning
Methodology
FV = PV×(1+r)^n + PMT×[(1+r)^n−1]/r (monthly compounding). Real return ≈ nominal rate − inflation rate (Fisher approximation).
Frequently Asked Questions
What is a realistic long-term investment return?+
The S&P 500 has returned approximately 10% annually before inflation over the past century, or about 7% after inflation. Individual stocks, bonds, and international equities vary. A diversified 60/40 portfolio has historically returned ~7–8% nominal.
What is the Rule of 72?+
Divide 72 by your annual return rate to estimate how many years it takes to double your money. At 8% per year, money doubles in roughly 9 years (72 ÷ 8). At 6%, it takes 12 years.
How does compound interest work in investing?+
Returns compound when gains are reinvested, earning future returns on top of prior gains. A $10,000 investment at 8% grows to $10,800 after year one. In year two, you earn 8% on $10,800 (not just $10,000), giving $11,664 — the extra $64 is compounding at work.
How much do I need to invest monthly to reach $1 million?+
It depends heavily on your time horizon and expected return. At a 7% annual return with no starting balance, investing about $1,230/month for 25 years grows to roughly $1 million. Starting earlier dramatically reduces the required monthly amount — at an 8% return over 35 years, roughly $435/month can reach $1 million — because more of the growth comes from compounding rather than new contributions.
What's the difference between nominal and real investment returns?+
Nominal return is your investment's growth rate before adjusting for inflation — the number typically quoted for a fund or index. Real return subtracts the inflation rate to show growth in actual purchasing power, using the approximation: real return ≈ nominal return − inflation rate. An 8% nominal return with 3% inflation is roughly a 5% real return, which is what actually determines how much more you can buy with your money in the future.
Is it better to invest a lump sum or dollar-cost average monthly?+
Historically, investing a lump sum immediately has outperformed dollar-cost averaging — spreading the same amount across several months — in a majority of historical periods, simply because markets trend upward over time and more money is invested for longer. However, dollar-cost averaging can reduce the risk and regret of investing a large sum right before a downturn, and it's the natural approach for anyone investing from ongoing income rather than a windfall.
Can I save my results?+
Yes. Use “Save results” to store a snapshot. Without an account it remains in this browser. If you log in, saved scenarios sync securely to your SmartRates account so they are available on your other devices.
How do I share my calculation?+
Click “Share” in the toolbar to copy a link (or open your device’s share sheet). The link encodes your exact inputs, so whoever opens it sees the calculator pre-filled with the same numbers and the same result.
Can I email my calculator results?+
Yes. Click “Email results” to open your default email application with the current inputs, results, and calculator link already included. Review the message and choose the recipient before sending.
Can I export or print my results as a PDF?+
Yes. Click “Export PDF” to open a clean, printable summary of your inputs and results that you can save as a PDF or print. It includes a timestamp and a link back to the calculator.
How accurate are the calculator results?+
The arithmetic follows the formula and assumptions documented on this page. The result is still an estimate because actual rates, fees, taxes, timing conventions, eligibility rules, and provider calculations can differ. Use figures from your official quote, statement, contract, or tax form before making a financial decision.
Which inputs have the biggest effect on the result?+
Rate, time, starting balance, recurring payments or contributions, and fees usually have the largest effects. Change one input at a time to create a conservative, expected, and optimistic scenario instead of relying on a single forecast.
Are taxes, fees, and inflation included?+
Only when they appear as an input or are explicitly described in the methodology. Do not assume an omitted cost is zero. Review the formula and methodology sections to see exactly what is included before comparing the result with an outside quote.
Can this calculator predict future rates or returns?+
No. A calculator projects the assumptions entered; it cannot predict market returns, inflation, variable interest rates, tax-law changes, or provider decisions. Rerun the calculation with several assumptions to understand the range of possible outcomes.
Why might my lender, bank, broker, or tax software show a different result?+
Professional systems may use daily timing, transaction dates, compounding conventions, rounding rules, account-specific fees, credits, eligibility details, or regulations that a general-purpose calculator cannot know. A small difference can be rounding; a large difference usually means an assumption or included cost is different.
Disclaimer: Calculations are for informational purposes only and do not constitute professional financial advice. Please consult with a certified professional before making financial decisions.