Your investment projection is "wrong" because it shows a single smooth line, while real markets deliver a bumpy path of gains and losses that can land far above or below that line. An investment calculator assumes the same return every year, but no portfolio earns exactly 7% twelve months in a row, year after year. The projected number is the midpoint of a wide range of possible outcomes, not a prediction. Here is what the smooth line hides — and how to read it honestly.
The midpoint is one number; reality is a fan of outcomes
A calculator that returns "$629,178" looks precise, but that precision is an illusion. The real future is a spread, and the inputs that move it are the same long-run averages applied to a path that never holds still. Take a $25,000 starting balance plus $600 a month for 25 years — $205,000 of your own money — and vary only the assumed annual return:
| Assumed return | Scenario | Ending balance |
|---|---|---|
| 4% | Pessimistic / bond-heavy | $376,322 |
| 5.5% | Below-average decades | $483,789 |
| 7% | Midpoint (real stock average) | $629,178 |
| 8.5% | Above-average decades | $826,995 |
| 10% | Optimistic / nominal average | $1,097,524 |
That is the honest picture: the same plan could realistically finish anywhere from about $376,000 to $1.1 million. The $629,178 midpoint is the most reasonable single guess, but treating it as a guarantee is how people end up disappointed — or dangerously under-saved.
Volatility drag: why the average year beats the average outcome
Here is a counterintuitive trap. The average of your yearly returns is always higher than the return you actually compound, and the more volatile the ride, the bigger that gap. This is volatility drag.
The classic illustration: a portfolio gains +50% one year and loses -50% the next. The arithmetic average is 0%, so you might expect to break even. You don't. Start with $10,000: it grows to $15,000, then falls by half to $7,500. You lost 25% despite a "0% average." The true compound (geometric) return was about -13.4% per year.
A milder, more realistic series — say +20%, -10%, +15%, -5%, +10% — averages 6.0% but compounds at only about 5.35%, a 0.65-point drag from the bumps alone. Calculators using a single smoothed rate already bake in the geometric (compound) figure, which is why you should feed them a CAGR-style number, not a simple average of yearly returns. Our guide on CAGR vs average annual return explains the difference in depth.
Sequence-of-returns risk: order matters more than you think
For a one-time lump sum, the order of returns is irrelevant — multiplication commutes, so a 30%/10%/-20% sequence ends at the same place as -20%/10%/30%. But the moment you add ongoing contributions (or withdrawals), the order of returns changes the outcome. This is sequence-of-returns risk, and it cuts in a direction that surprises most people.
Contribute $10,000 at the start of each year for three years, using the same three returns in two different orders:
| Return order | Year-by-year | Ending balance |
|---|---|---|
| Gains first | +30%, +10%, -20% | $28,240 |
| Losses first | -20%, +10%, +30% | $38,740 |
Same three returns, same money in — yet a $10,500 difference. While you are accumulating, a downturn early is actually good: your contributions buy in cheap and then ride the recovery up. The danger flips in retirement: once you are withdrawing, an early downturn forces you to sell more shares at low prices, permanently shrinking the pot. A flat midpoint projection shows none of this, which is why retirees especially need stress-testing, not a single line. See the retirement withdrawal calculator for the decumulation side.
Inflation: the quiet erosion under every nominal projection
If your projection uses a nominal return like 10%, remember the ending number is in future dollars that buy less than today's. About $1.33 million in 30 years, deflated at 3% inflation, has the buying power of roughly $547,000 today. That is not a small footnote — it is nearly 60% of the headline number evaporating into purchasing-power loss. Either project with a real return (about 7%) from the start, or run your nominal result through the inflation calculator to see it in today's money.
How to make your projection honest
- Project a range, not a point. Run a pessimistic, midpoint, and optimistic rate — for example 4%, 7%, and 10% — and plan around the conservative end.
- Use a real return for spending goals. A 7% real rate already removes inflation; a 10% nominal rate doesn't.
- Feed it a compound rate. Use a CAGR-style figure, not a simple average of yearly returns, so volatility drag is already accounted for.
- Stress-test the withdrawal years. If money will be drawn down, model an early-downturn scenario, not just the average.
- Re-run it yearly. Update with your real balance each year so the projection tracks reality instead of drifting.
An independent reference on market risk
Volatility and sequence risk are not pessimism — they are the documented behavior of markets. For an ad-free, official explainer on investment risk and why returns vary, the U.S. Securities and Exchange Commission's Investor.gov is a solid starting point. To pressure-test long-horizon plans, pair the investment calculator with the retirement calculator and the FIRE calculator.
Read the midpoint as a midpoint
The number an investment calculator shows is genuinely useful — as the center of a range, fed an honest compound rate, adjusted for inflation, and stress-tested for bad timing. Treat it that way and the projection stops being "wrong" and starts being a real planning tool.
Try it yourself
Run your own numbers in the free Investment Calculator — instant, private, no sign-up.
Open the Investment Calculator →Frequently asked questions
- Why is my investment projection different from my actual returns?
- Your projection assumes the same smooth return every year, but real markets deliver bumpy gains and losses that rarely match the average in any single year. The projected figure is the midpoint of a wide range, not a prediction. Over a 25-year plan, the same contributions could realistically finish anywhere from well below to well above the midpoint.
- What is volatility drag in investing?
- Volatility drag is the gap between the average of your yearly returns and the lower return you actually compound, caused by ups and downs. A portfolio that gains 50% then loses 50% has a 0% average but turns $10,000 into $7,500, a real compound return of about -13.4%. The bumpier the ride, the larger the drag, so always use a compound (CAGR) rate.
- What is sequence-of-returns risk?
- Sequence-of-returns risk is the danger that the order of good and bad years, not just their average, changes your outcome once you are adding or withdrawing money. For a lump sum the order does not matter, but with contributions or withdrawals it does. An early downturn helps while you save but badly hurts once you are drawing the money down in retirement.
- Does the order of returns matter for a lump sum?
- No, for a single lump sum the order of returns does not matter, because multiplying the same growth factors in any order gives the same result. A 30%, 10%, -20% sequence ends at the same balance as -20%, 10%, 30%. Order only changes the outcome once you add ongoing contributions or withdrawals to the mix.
- Should I trust the single number an investment calculator gives me?
- Trust it as a midpoint, not a guarantee. The real future is a range driven by which years are good or bad and in what order. Run a pessimistic, middle, and optimistic rate, use a real return for spending goals, and re-run the projection yearly with your actual balance so it tracks reality.
- How does inflation affect my projection?
- Inflation quietly shrinks the buying power of any nominal projection. About $1.33 million in 30 years, deflated at 3% inflation, has the purchasing power of roughly $547,000 today. To avoid the illusion, project with a real return of about 7% from the start, or run your nominal result through an inflation calculator to see it in today's dollars.
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