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The Behaviour Gap
Two people. Same salary, same market, same fund, same 30 years. One holds through every storm. The other sells when it is frightening and buys when it feels safe. The gap between them is the most expensive and most avoidable number in personal finance.
The good news is hiding inside that number: it is the one investing cost you can close for free. Not with more effort, but with less.
How big is the gap really? The famous figures cannot be recomputed from their published methods, so in 2026 I rebuilt it from 341,049 public SEC filings, with the data and code published alongside — the working paper is here. Set any of its numbers in the calculator below.
Disciplined
$0
Emotional you
$0
The gap = the cost
$0
When a crash hits, how do you react?
This is the only thing you control. Everything the market does is real history — the crashes actually happened. All you decide is how hard you flinch when they do.
Your money
The photo finish
—
Pick a reaction above, then press start and watch the two of you run.
Market path: approximate S&P 500 total returns, 1995–2024. The panic effect (selling into crashes, missing the rebound) is a simplified rule for illustration — real behaviour is messier. An annual view even hides the 2020 COVID crash, which fell ~34% and recovered inside the year: itself a lesson in not reacting. Excludes tax, fees and inflation. Not financial advice.
The third thief
There are three forces quietly removing money from your portfolio. Two of them are visible and much discussed. Inflation erodes what your money buys, at around 2% a year. Fees come straight off your return, typically a fraction of a percent to well over one percent. Both matter, and both have a calculator here: inflation and fees.
The third thief is the one nobody puts on a statement, because it does not appear on one: your own behaviour. It is the return you give up by acting on emotion: buying after the crowd, selling into fear, sitting in cash waiting for certainty. And it is usually the biggest of the three.
The number that should stop you — and the one to check it against
The figure you will have heard is DALBAR's. In 2024 the S&P 500 returned 25.02%; the average equity investor, on its measure, earned 16.54%, a gap of 8.48 percentage points in a year the market went straight up. One year later the same study put the gap at 0.72. A number that moves by a factor of twelve in twelve months is measuring the market that happened at least as much as the people in it — and it cannot be recomputed, because the method is not published.
So I rebuilt the measure from public SEC filings. Across 7,073 US funds and 341,049 filings, the base-case gap for 2020 to 2025 comes out at 0.36 points a year, and it lands anywhere between −0.06 and +0.62 depending on a single share-class assumption the famous figures never state. The paper, the data and the code are at /research/behaviour-gap. The direction survives; the size, in most measurements, is far smaller than the seminar slide.
A single year is noise. The point is what that behaviour does when it repeats. Pick a reaction, press start, and watch the two of you run through 30 real years — dot-com, 2008, 2022. The shaded gap that opens up is not a market loss. It is the same money, handed back voluntarily, in a handful of frightened moments.
Why this is the good news
Inflation and fees are largely outside your control. The behaviour gap is almost entirely inside it, which makes it the most fixable cost you will ever face. You do not close it by being smarter or watching more closely. You close it by removing the moments where emotion gets a vote: automate the buying, decide the rules in advance, and then leave the plan alone.
That is the entire argument of the Real Life Scenarios series, from why willpower fails to the three-check routine professionals run before every trade. The disciplined line in the chart above is not a reward for brilliance. It is the reward for being deliberately, profitably boring.
What this deliberately ignores
- Timing of the damage. Real behaviour gaps are episodic rather than smooth, concentrated in a few crashes. The reaction rule here is a simplified stand-in, for clarity, not precision.
- Tax and inflation. Both further reduce what the final figures are worth to you. Use the inflation calculator alongside this one.
- That some gaps are rational. Selling for a genuine life reason is not a behaviour gap. The gap is the cost of selling for an emotional one.
The good news
The one cost you can simply decide to stop paying.
You do not close the gap by watching more closely or being smarter. You close it by removing the moments where emotion gets a vote — deciding the rules once, while you are calm, and then being deliberately, profitably boring. Here is exactly how the professionals do it.
The 3-check routine
The exact pre-trade checklist professionals run, so no decision is ever made in the heat of the moment.
ReadSystems over willpower
Why discipline you have to summon fails — and the structure that quietly does the work for you.
ReadRules over access
How the biggest fund on earth stays calm: a written mandate, followed for years without flinching.
Questions people actually ask
What is the behaviour gap?
The behaviour gap is the difference between the return an investment earns and the return the investor in it actually captures. The investment does not lose the money — the investor does, through timing: buying after a rally, selling in a panic, waiting for a "better moment" that never comes. DALBAR, which has measured this for decades, found the average US equity investor earned 16.54% in 2024 against the S&P 500’s 25.02% — a gap of 8.48 percentage points in a single positive year. That figure cannot be recomputed, because the method is not published in reproducible detail. A rebuild from 341,049 public SEC filings, published on this site with its data and code, puts the base-case gap across 7,073 US funds at 0.36 percentage points a year for 2020 to 2025, with a defensible range of −0.06 to +0.62 depending on which share class is assumed to stand in for the fund. Even the smaller gap compounds over a lifetime, which is what this simulator shows.
Is this based on real market history?
Yes. The market path is the approximate total return of the S&P 500 for each year from 1995 to 2024 — a real 30-year run that includes the dot-com bust, the 2008 financial crisis and the 2022 selloff. You do not invent the returns; you only choose a reaction level — how hard you flinch when the crashes arrive. The reaction itself is a simplified rule — selling into the fall and missing part of the rebound — because real behaviour is messier than any formula. It is honest enough to make the point without pretending to predict exactly when anyone panics.
Why does the gap matter more than fees or inflation?
Because it is larger and it is optional. A typical fund fee costs perhaps 0.2% to 1.5% a year, and inflation erodes purchasing power at around 2%. A behaviour gap of 2.5% a year — well within the measured range — exceeds either, and unlike the other two you are not obliged to pay it. Fees and inflation are largely outside your control. The behaviour gap is almost entirely inside it, which is what makes it the most fixable cost in investing.
How do I actually close my behaviour gap?
By removing the moment of decision. The reliable fixes are structural, not motivational: automate your contributions so money is invested before you can hesitate, write down in advance the rules under which you will buy or sell, and then deliberately do nothing between those triggers. Professionals prize a low activity ratio — fewer trades, not more. The disciplined line in this chart is not the reward for being clever; it is the reward for being boring on purpose.
Sources — retrieved August 2026
- The gap, rebuilt from public data: One Gap, Three Readings — a money-weighted investor return for 7,073 US funds from 341,049 SEC N-PORT filings, 2020–2025; base case +0.36 points a year, range −0.06 to +0.62 depending on the share class assumed. Data and code published — Philipp Misura, ProfitOwl Research, September 2026, working paper
- The gap as usually quoted: Quantitative Analysis of Investor Behavior (QAIB) — fund returns against what investors actually earned; the method is not published in reproducible detail — DALBAR, published annually since 1994
- Market path: S&P 500 total returns by calendar year, 1995–2024 — S&P Dow Jones Indices data, compiled by Slickcharts, 1926–2026
- Why timing rarely helps: SPIVA Scorecards — active funds against their benchmarks — S&P Dow Jones Indices, updated semi-annually
The famous gap figures cannot be recomputed: DALBAR does not publish its method in reproducible detail, and Morningstar's version runs on licensed data. So in 2026 I rebuilt the measure from public SEC filings and published the data and code alongside. That rebuild puts the base-case gap at 0.36 points a year, far below the quoted figures, and shows the number swinging between −0.06 and +0.62 on one share-class assumption alone. The simulator here does not use any of those figures as an input — it models the behaviour that produces a gap, and lets you choose how strongly you react.
What this tool is — and what it is not
- Runs in your browser
- Your numbers are never sent anywhere. There is no account, no sign-up and no server doing the maths. Analytics are cookieless and EU-hosted, and your IP address is not stored. The full privacy detail →
- Nothing to sell
- No course, no recommendation, no affiliate links, no ads. If that ever changes, it will say so here before it says so anywhere else.
- Not financial advice
- This is a model, not a personal recommendation. It does not know your tax position, your job security or how well you sleep. A decision this size belongs in a conversation with someone licensed to advise you.
- Who built it
- Philipp Misura — Nearly two decades in the financial industry — first inside the institutions, then advising them. More about Philipp →