Benchmarking

Why most private investors underperform (and the boring fix)

The market returns X. The funds tracking it return almost-X. The people in those funds reliably earn less than the funds themselves. That last gap, the behavior gap, has been measured for thirty years, lands between one and two percent annually, and is entirely self-inflicted.

Read that middle sentence again, because it's the strange one. These investors are not picking bad funds. They are earning less than the funds they actually hold, which means the entire shortfall is generated by the timing of their own deposits and withdrawals. The vehicle was fine. The driving wasn't.

What the gap actually measures

The behavior gap is the distance between two return numbers computed from the same account. A fund's published return is time-weighted: it measures what the fund did, indifferent to when anyone's money arrived. An investor's personal return is money-weighted: every euro counts for exactly as long as it was invested, so late arrivals and early exits leave fingerprints. When money habitually shows up after the good returns and leaves before the recovery, the money-weighted number falls below the time-weighted one, and the difference is the gap. The full mechanics of the two measures are laid out in time-weighted vs money-weighted return; the short version is that the gap is your timing, isolated from your picks, expressed as a percentage you personally donated.

Research on investor behavior consistently finds the same signature across countries, decades, and fund types, in dull index funds and racy sector funds alike, with the gap generally widest in the most volatile funds. Volatility creates the temptation, and the temptation gets taken.

Where the money leaks

Buying excitement. Money floods in after rallies, at exactly the prices that make future returns smaller. Deposits during fear, the mathematically attractive moment, take actual discipline.

Selling winners, keeping losers. Taking profits feels responsible; realizing losses feels like admitting failure. The result is a portfolio that systematically sheds what works and preserves what doesn't. The accounting distinction that enables the self-deception, treating a loss as somehow not real until you sell, is dissected in realized vs unrealized gains.

Activity itself. The classic Barber & Odean finding: the more retail investors trade, the worse they do. Every trade is a fee, a spread, and a fresh chance to be wrong.

Untracked experiments. The crypto phase, the leveraged ETF week, the options month. Individually small, collectively a silent percent a year, invisible because nobody's adding them up. These often live at a second or third broker precisely so they don't contaminate the "real" portfolio's statistics, which is why pulling every account into one dashboard is less a convenience than an integrity measure.

Why intelligent people keep doing this

None of these leaks come from stupidity; they come from standard-issue human wiring meeting a domain that punishes it. Losses hurt roughly twice as much as equivalent gains feel good, so realizing a loss gets postponed indefinitely while gains get harvested for the small dopamine of being right. Recent events dominate our sense of the future, so a market that just rose feels safer, exactly backwards, given prices. And nearly everyone rates their own judgment above average, so each trade feels like the exception to statistics that were, in fairness, compiled from other people's trades.

Markets are one of the few environments where the intuitive move is reliably the expensive one. Feeling confident arrives after prices rise; feeling sick arrives after they fall. An investor who simply obeys those feelings ends up buying high and selling low with impeccable emotional logic. The behavior gap is what that logic costs at scale.

A small example of the boring alternative

Dollar-cost averaging, buying a fixed amount on a fixed schedule, is usually sold as a comfort blanket. It's actually a small arithmetic machine. Suppose you invest €300 a month in a fund whose price goes €10, €12, €8 over three months. You buy 30 shares, then 25, then 37.5: 92.5 shares for €900, an average cost of about €9.73 per share, below the €10 average of the three prices.

That's not luck; it's mechanics. A fixed euro amount buys fewer shares when they're expensive and more when they're cheap, automatically leaning the right way, which is precisely the direction emotions lean wrong. The point isn't that averaging in beats a lump sum, over long periods, markets rise, so earlier money tends to do better, it's that a standing order executes on schedule whether you're euphoric or terrified, and the behavior gap lives entirely in the difference between those two states. What steady contributions do over decades is its own quietly impressive story, told in the compound math of monthly investing.

The unglamorous fix

Nothing here is solved by trading smarter. It's solved by seeing clearly and automating the boring parts: automatic monthly buys (removes timing emotion), one honest dashboard including closed positions and fees (removes selective memory), and a real benchmark, your own cash flows replayed into an index, so every decision faces the question "did this beat doing nothing?"

That last one changes behavior more than any market opinion. When the ghost portfolio is always on screen, impulse trades have to argue with evidence.

Notice that all three fixes share a design principle: they remove decisions rather than improve them. This is what most investors get backwards. The instinct after discovering underperformance is to try harder, more research, more screens, more conviction, which increases the number of decisions and therefore the number of opportunities for the wiring to fire. The fix that works runs the opposite direction: fewer moments where a feeling can become a trade. It's not inspiring. It compounds.

Finding your own number

Averages are comfortable to read and useless to act on; the question that pays is whether you have a gap, and how big. The audit takes two comparisons. First, your money-weighted return against your time-weighted return: if the money-weighted number sits persistently lower, your timing has been taxing your own holdings, and the size of the difference is roughly the annual rate of the tax. Second, your time-weighted return against an index you'd actually buy instead: that one grades the picks themselves.

Both comparisons need your complete history, deposits, withdrawals, every closed position, the fees, the experiments, because the leaks live disproportionately in the parts memory has already discarded. A portfolio review that only covers the positions still open is a crime scene with the evidence removed. The good news is that the complete history already exists, timestamped, in the transaction export your broker will hand you in about four clicks. Nobody enjoys the first look. Everyone is better off after it.

Measurement is the intervention

There's a reason the fund manager's behavior gap is smaller than the amateur's, and it isn't talent: it's that someone is watching. Reported numbers, compared against a benchmark, on a schedule, discipline behavior all by themselves. A private investor can rent the same effect for the price of looking at an honest dashboard, one that includes the sold positions, the fees, the experiments at the second broker, and the ghost portfolio that made no decisions at all, using the method described in how to check if you're beating the S&P 500.

BullBenchmark exists to be that mirror: your full history, all brokers, benchmarked daily. It won't make you Warren Buffett. It makes you measured, and measured investors, the data says, leak less.

The first week of BullBenchmark is free, no card, upload the export you just downloaded and see where you stand.