Three ways to measure and model investment returns
The calculator offers three modes because investment return questions come in three flavours. Mode A — “What return did I get?” works backwards from what you started with and what you ended with to give you the actual annualized rate. If you added money along the way it uses a money-weighted return (IRR), which is the standard used by investment professionals because it accounts for the timing of each deposit.
Mode B — “What will it grow to?” is a forward projection: enter a starting amount, monthly contribution, annual return assumption, and time horizon to see the ending value. This mode uses the same end-of-period monthly compounding engine as the compound interest calculator — use that tool when your primary goal is modeling future growth rather than measuring a past return.
Mode C — “S&P 500 backtest” answers the “what if I’d just bought the index?” question. It uses annual compounding at the historical average nominal rate (default 10%) and shows the inflation-adjusted real value alongside. The disclaimer is not boilerplate: historical averages hide multi-year drawdowns of 30–50%, and past performance is not a guarantee of future results.
ROI vs CAGR vs money-weighted return: which should you use?
Total ROI is the simplest measure: (ending value − total invested) ÷ total invested. It tells you the overall gain as a percentage but ignores time entirely. A 100% ROI over 2 years is very different from the same gain over 20 years.
CAGR (compound annual growth rate) is the right comparison tool for lump-sum investments across different time periods. It answers: “what single annual rate, compounded each year, gets from start to end?” Use it to compare your stock pick against an index, or two funds with different inception dates.
Money-weighted return (IRR) is the most accurate measure when contributions varied over time. It gives more weight to periods when you had more money invested. If you deposited a large lump sum right before a strong year, your money-weighted return will be higher than the simple CAGR of the fund itself — because you personally benefited from that timing. Enter your monthly contributions in Mode A and the calculator switches to IRR automatically.
Planning future growth instead?
Mode B above gives you a quick projection, but for a full planning experience — inflation toggle, rate variance band, cost-of-waiting visualizer, and a year-by-year breakdown — use the dedicated tools:
- Compound Interest Calculator → The flagship for modeling savings + contributions over any horizon.
- Investment Growth Calculator → Focused on investment-specific framing with contribution schedules.
How the S&P 500 backtest works — and its limits
Mode C uses annual compounding at your chosen nominal rate (default 10%, the approximate S&P 500 long-run average) to compute a headline ending value. It also shows the real value at a lower rate (default 7%) to represent purchasing power in today’s dollars.
What the model does not show: sequence-of-returns risk. A 10% average can look very different depending on when you start and stop. Someone who retired in 1999 and withdrew through the 2000–2002 and 2008–2009 crashes experienced a very different outcome than the long-run average suggests. For retirement planning, use the retirement calculator which models drawdown sequences and safe withdrawal rates.
The backtest is useful for one thing the long-run average is good at: showing the compounding power of time. Whether you invested $10,000 for 10 years or 30 years at the same rate, the difference is dramatic — and the “Started 10y earlier” What-If chip makes that concrete instantly.
The hidden cost of fees
The “After 2% fees” chip in Mode A is one of the most important scenarios to run. A 2% annual expense ratio — common in actively managed funds — reduces your effective return by 2 percentage points every year. At 8% gross, you earn 6% net. Over 20 years on a $50,000 investment, that difference compounds to tens of thousands of dollars.
Index funds typically charge 0.03–0.20% per year. If your current investment earns 8% gross and you’re paying 1.5% in fees, your real return is about 6.5%. Enter your actual gross return in Mode A and hit “After 2% fees” to see exactly what that drag costs you over your specific time horizon.
Frequently asked questions
How do you calculate investment return?
There are two main measures. Total ROI is simply (ending value − amount invested) ÷ amount invested. Annualized return (CAGR) adjusts for time: (end / start)^(1/years) − 1. When you added money along the way, the money-weighted return (IRR) is the most accurate — it accounts for the timing of each contribution. The calculator picks the right method automatically: CAGR for lump sums, IRR when you enter monthly contributions.
What is a good ROI on an investment?
It depends entirely on the asset class and your time horizon. Broad U.S. stock market indexes have averaged roughly 10% per year (nominal) or about 7% after inflation over very long periods — that's a common benchmark. Cash and CDs offer lower but guaranteed returns. Real estate, bonds, and alternatives sit in between. A "good" ROI is one that fairly compensates for the risk and illiquidity you took on.
What is the difference between ROI and annualized return (CAGR)?
ROI tells you the total percentage gain over the whole period, regardless of how long it took. CAGR (compound annual growth rate) expresses that same gain as an equivalent annual rate — so you can compare investments held for different lengths of time. A 100% total ROI over 5 years is a 14.87% CAGR; over 10 years it is only 7.18%. Always compare annualized returns when comparing across different time horizons.
What is the average stock market return over 30 years?
The S&P 500 has returned approximately 10% per year on average in nominal terms over long 30-year rolling windows, or roughly 7% after inflation. However, any individual 30-year window can vary significantly — some start near a peak, others near a trough. The S&P 500 backtest mode (Mode C) uses these long-run averages and clearly labels them as historical estimates, not guarantees.
Is a 7% return realistic for long-term investing?
Yes — 7% is the approximate real (inflation-adjusted) long-run average of the U.S. stock market, and many financial planners use it as a conservative planning assumption. In nominal terms the average is closer to 10%, but inflation erodes purchasing power. For retirement planning, using the real rate (7%) gives you a more honest picture of what your money will actually buy in the future.
Worked examples
Each result is computed by the same engine that powers the calculator. Return assumptions are historical averages or user-supplied planning figures — not predictions.
Five-year stock position
$12,000 invested in a broad index fund, grown to $21,500 over 5 years with no additional deposits.
- Starting value
- $12,000
- Ending value
- $21,500
- Holding period
- 5 yrs
- Total ROI
- 79.2%
A 79.2% total ROI over 5 years converts to a 12.37% annualized return — well above the S&P 500 long-run average of ~10%. The annualized figure is what lets you honestly compare this against any other investment.
Ten-year bond portfolio
$30,000 in a bond ladder, ending at $43,200 after 10 years. No mid-period additions.
- Starting value
- $30,000
- Ending value
- $43,200
- Holding period
- 10 yrs
- Total ROI
- 44.0%
A 44% total gain over 10 years is a 3.73% CAGR — near the long-run nominal return of a medium-duration investment-grade bond fund. Low by equity standards, but appropriate compensation for much lower volatility.
S&P 500 backtest: $10,000 for 20 years
Lump-sum $10,000 at the historical long-run S&P 500 average — 10% nominal, 7% real.
- Lump sum
- $10,000
- Horizon
- 20 years
- Nominal gain
- $57,275
The gap between nominal ($67,275) and real ($38,697) illustrates how inflation silently erodes what a large nominal gain actually buys. Both numbers are historical averages — not a forecast.
Historical average — not a forecast. Past S&P 500 performance does not guarantee future results. Excludes fees, taxes, and sequence-of-returns risk.
CAGR by total return × holding period
What annualized return does a given total gain represent at each holding period? Starting value $10,000 in all cells.
| Total return | 1 yr | 3 yr | 5 yr | 10 yr | 20 yr |
|---|---|---|---|---|---|
| +25% total | 25.00% | 7.72% | 4.56% | 2.26% | 1.12% |
| +50% total | 50.00% | 14.47% | 8.45% | 4.14% | 2.05% |
| +100% total | 100.00% | 25.99% | 14.87% | 7.18% | 3.53% |
| +200% total | 200.00% | 44.22% | 24.57% | 11.61% | 5.65% |
| +500% total | 500.00% | 81.71% | 43.10% | 19.62% | 9.37% |
A 100% total gain (2× money) over 5 years = 14.87% CAGR; the same gain over 10 years = only 7.18%. Time is the critical input when annualizing any return.
What affects your results
These inputs move the needle most — ranked by their leverage on the final outcome. All rate inputs are user-supplied; this calculator does not access live market data.
Holding period is the most underestimated variable in annualized return. A 50% total gain over 2 years is a 22.5% CAGR; over 10 years it is only 4.14%. Because CAGR is exponential, even a 1-year difference in holding period changes the annualized figure significantly on shorter horizons.
The starting value is as important as the ending value. Buying at a high price — near a market peak — reduces your measured return even if the absolute gain was identical to someone who bought at a trough. This is why CAGR comparisons between different investors with different start dates are often misleading.
When monthly contributions are entered, the calculator switches from CAGR to IRR (money-weighted return). IRR is sensitive to when each deposit was made — contributing large amounts just before a market drawdown lowers the IRR even if the portfolio eventually recovered, because more dollars were exposed to the downturn.
Reinvested dividends are not visible in price charts but they account for roughly 40% of the S&P 500's long-run total return. If your "ending value" comes from a price-only source (not total return), you are understating your actual CAGR. Always use the total-return ending value, which assumes dividends were reinvested.
Common mistakes to avoid
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Comparing total ROI across investments with different holding periods. A 40% gain over 1 year and a 40% gain over 5 years are not equivalent. Always convert to annualized return (CAGR) before comparing.
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Using the stock's price change as the ending value when the investment paid dividends. This understates total return. Use the total-return ending value (your actual brokerage account balance) as the ending figure.
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Confusing this tool with a forward projection calculator. This calculator measures returns you have ALREADY earned — it is backward-looking. For "what will $X grow to?", see the compound interest or investment projection calculator.
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Entering years as a decimal when the holding period was months. The calculator supports decimals (e.g. 2.5 for 30 months), but rounding to the nearest whole year introduces error on shorter horizons. Be precise.
Key takeaways
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Use CAGR as your headline comparison metric. It normalizes for time, letting you rank a 2-year trade, a 5-year fund hold, and a 10-year real estate investment on the same axis.
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Check your return against appropriate benchmarks — not just the S&P 500. Bonds should be compared to bond indices; real estate to REIT indices. Beating a low-volatility benchmark by 2% is a different achievement than beating it with four times the volatility.
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If you added money along the way, use the money-weighted return (IRR) tab — not CAGR. CAGR applies only to a single starting investment with no mid-period cash flows. The calculator switches automatically when you enter monthly contributions.
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For retirement-planning decisions, run this calculator alongside the retirement calculator to see whether your historical return is tracking toward your goal — or whether you need to adjust contributions.
Key terms
- ROI (Return on Investment)
- The total percentage gain on an investment: (ending value − amount invested) ÷ amount invested. ROI ignores time — a 50% gain over 1 year and a 50% gain over 10 years both show as 50% ROI, even though the first is far better on an annual basis.
- CAGR (Compound Annual Growth Rate)
- The constant annual rate that would take your starting value to your ending value over the same number of years. Formula: (End / Start)^(1/Years) − 1. CAGR removes the distortion of time and lets you compare investments held for different lengths.
- IRR (Internal Rate of Return)
- The annualized rate that sets the net present value of all cash flows to zero — effectively the money-weighted return. Unlike CAGR (which ignores timing), IRR accounts for when each contribution or withdrawal happened, making it the most accurate measure when you added money along the way.
- Annualized Return
- Any return expressed as an equivalent per-year rate, regardless of the actual holding period. CAGR is the standard annualized return for lump-sum investments. IRR is the annualized money-weighted return when contributions or withdrawals occurred. Both allow apples-to-apples comparison across different time horizons.
- Total Return
- The complete gain from an investment including both price appreciation and any income (dividends, interest, distributions). The S&P 500's well-cited ~10% historical average is a total-return figure — it assumes dividends are reinvested. Price appreciation alone is roughly 6–7% per year.
- S&P 500 Historical Assumption
- The long-run average nominal return of the S&P 500 is approximately 10% per year, with a real (inflation-adjusted) average of ~7%. These are planning proxies derived from rolling 30-year windows — not guarantees. Any given 10-year period has ranged from roughly −1% to +19%. Past performance does not predict future results.
- Holding Period
- The length of time an investment is owned before it is sold. Holding period matters for two reasons: (1) CAGR is sensitive to it — a 100% gain in 5 years is 14.87% annualized, but the same gain over 10 years is only 7.18%; (2) taxes — in the US, gains held more than one year qualify for lower long-term capital gains rates.
- Money-Weighted Return (MWR)
- The IRR of all cash flows into and out of a portfolio. Unlike time-weighted return (TWR), MWR is sensitive to timing — large contributions just before a market drop hurt the MWR more than TWR. This calculator uses MWR/IRR when monthly contributions are entered, because it reflects the return actually earned on the actual dollars invested.
More questions answered
How do you calculate ROI?
ROI (return on investment) = (final value − amount invested) ÷ amount invested. If you invested $10,000 and your portfolio is now worth $13,500, ROI = ($13,500 − $10,000) ÷ $10,000 = 35%. ROI ignores how long you held the investment — which is why CAGR (annualized return) is more useful for comparisons.
What is a good return on investment?
It depends on the asset class. Broad U.S. equity indexes have averaged ~10% nominal / ~7% real over long periods. Investment-grade bonds average 3–5% nominal. Cash and CDs offer lower but near-guaranteed returns. A "good" return is one that adequately compensates for the risk and illiquidity you took on — not just a high number in isolation.
What is the difference between ROI, CAGR, and IRR?
ROI is the total percentage gain over the whole holding period, ignoring time. CAGR is the constant annual rate that produces the same total gain — it normalizes for time. IRR (internal rate of return) is the annualized money-weighted return when cash flows in or out at multiple points; it accounts for the timing of each contribution or withdrawal. Use ROI for a quick snapshot; CAGR for comparing single-period returns; IRR for portfolios with ongoing contributions.
What does a 20% ROI mean?
A 20% ROI means your investment returned $0.20 for every $1 you put in — a $10,000 position is now worth $12,000. Annualized, a 20% total ROI over 1 year is a 20% CAGR; over 5 years it is only a 3.71% CAGR; over 10 years it is a 1.84% CAGR. Always specify the holding period alongside any ROI figure.
Can I use this calculator for real estate ROI?
Yes for the appreciation portion: enter your purchase price as starting value and current market value as ending value. However, real estate total return includes rental income, tax deductions, leverage effects, and ongoing costs (maintenance, taxes, insurance) that this calculator does not model. For a complete real estate ROI, you need a dedicated rental property calculator that accounts for cash-on-cash return and cap rate.
How is this different from the average return on a Roth IRA?
A Roth IRA is a tax wrapper, not an investment. The return inside a Roth depends entirely on what you invest in — if it holds a broad S&P 500 index fund, the historical average is ~10% nominal. Use this calculator to measure the actual return on whatever is inside your Roth (enter start and end balances). For modelling whether your Roth IRA will fund retirement, use the retirement calculator instead.
What is the S&P 500 historical return over 30 years?
The S&P 500 has returned approximately 10% per year in nominal terms over rolling 30-year windows historically, and roughly 7% in real (inflation-adjusted) terms. Any specific 30-year period varies — some begin near peaks (lower outcome), others near troughs (higher outcome). The backtest mode in this calculator uses these long-run averages and clearly labels them as historical planning estimates, not guarantees.