Investor BehaviorExplainer
What is overconfidence bias, and how can it cost investors money?
Overconfidence bias means trusting your own knowledge or skill more than the facts support. See survey data, how it leads to over-trading, and simple checks.
Quick answer
Overconfidence bias is believing your knowledge, skill or predictions are better than they really are. In investing it can lead to trading too often, putting too much money in a few holdings and missing warning signs of fraud.
Key points
- An SEC-commissioned report calls overconfidence an emotion common among investors that triggers a wide range of investment errors.
- In a 2024 FINRA Foundation survey, 56% of investors rated their own knowledge highly, but respondents answered 5.3 of 11 quiz questions correctly on average.
- Among investors who feel highly knowledgeable, 51% could not identify the warning signs of fraud in that survey.
- Frequent trading adds costs; in our illustration, 24 round trips a year at 0.25% each turns about $17,908 into about $9,821 over 10 years.
- Simple habits — writing down your reasons, limiting position sizes and comparing your results with a plain index — help keep confidence honest.
What is overconfidence bias?#
Overconfidence bias is the gap between how good we think our judgment is and how good it actually is. The 2010 report on investor behavior that the Library of Congress prepared for the SEC describes overconfidence as an emotion common among investors that triggers a wide range of investment errors[1].
One way researchers measure it is simple. A FINRA Foundation study compared how confident people were about their financial knowledge with how they actually scored on a quiz; by subtracting literacy scores from confidence scores, it quantified each person's level of overconfidence[2]. A high score means confidence runs ahead of knowledge.
Overconfidence can take several forms. You may believe you know more than you do, that you can predict prices better than you can, or that your past wins came from skill rather than luck. Each one makes risk feel smaller than it is.
What does survey data show about investor confidence?#
The FINRA Investor Education Foundation's 2025 report on U.S. investors draws on a 2024 survey of 2,861 investors[3]. A majority, 56%, rated their own investment knowledge highly — 5 to 7 on a 7-point scale. Yet respondents answered slightly less than half of the investing quiz questions correctly, 5.3 out of 11 on average[3].
Confidence vs knowledge: FINRA Foundation survey of U.S. investors (2024 data)
The people who rated themselves highly did score better — 6.0 correct versus 5.0 for those with neutral self-ratings[3]. In percentage terms that is 54.5% versus 45.5%: better, but far from the expertise a top rating suggests. A separate FINRA Foundation brief found the same pattern among investors who use social media for investment decisions: 63% of users reported high subjective knowledge versus 53% of non-users, while users answered 42% of quiz questions correctly versus 47% for non-users[4].
Worked example
Worked example: turning quiz scores into percentages
The survey reports average correct answers out of 11 questions. Dividing by 11 makes the gap between self-image and results easier to see.
| Group in the 2024 survey | Average correct | Share correct |
|---|---|---|
| All respondents | 5.3 of 11 | 48.2% |
| Investors who rate their knowledge highly | 6.0 of 11 | 54.5% |
| Investors with a neutral self-rating | 5.0 of 11 | 45.5% |
Figures computed in code from the stated inputs; rounded to the nearest cent or tenth.
How does overconfidence lead to trading too much?#
If you believe you can spot the next move, trading often feels like using your edge. The SEC's bulletin on investor behavior describes active trading — regular, ongoing buying and selling — and reports the finding that active trading generally results in the underperformance of an investor's portfolio[5]. In the 2024 survey, 36% of respondents reported making four or more trades in the past year[3].
Each trade can also carry costs. Even when commissions are low, the bid (the highest price a buyer will pay) and the ask (the lowest price at which a seller will sell) differ, and that difference is called the spread[6]. In U.S. taxable accounts, gains on assets held one year or less are short-term and taxed as ordinary income[7]. FINRA's required day-trading risk statement is blunt: day trading can be extremely risky, and it will generate substantial commissions, even if the per trade cost is low[8]. See why market timing is hard for the tax side.
| Round trips per year | Yearly cost drag | Balance after 10 years |
|---|---|---|
| No trading (buy and hold) | 0.00% | $17,908.48 |
| 2 round trips a year | 0.50% | $17,034.00 |
| 12 round trips a year | 2.96% | $13,261.94 |
| 24 round trips a year | 5.83% | $9,821.00 |
Computed in code. The 6% gross return and 0.25% cost per round trip are assumptions for illustration, not measured figures or a forecast. Real costs vary with the investment, the firm and the account.
The illustration assumes every trade earns the same return as doing nothing, which is generous to the trader. It shows how a small cost repeated many times compounds against you — the same arithmetic covered in how investment fees affect returns.
Where else does overconfidence show up?#
Trading is not the only symptom. The same SEC bulletin describes familiarity bias — the tendency to favor investments from your own country, region, state or company, or well-known "glamour" investments — and says it may leave a portfolio inadequately diversified, which can increase risk[5]. Feeling that you understand a few companies well can make it seem safe to bet heavily on them. Investor.gov warns that it can be risky to invest heavily in shares of any individual stock[9].
Overconfidence also changes how much risk people take. The FINRA Foundation study of older adults found that individuals with the highest overconfidence scores reported being more willing to take financial risks[2]. Our note on diversification explains why spreading money out reduces the damage when any one judgment turns out wrong.
| Sign | What it can cost | A check |
|---|---|---|
| Trading often on hunches | Costs, taxes, and selling good holdings too early | Count your trades for a year and total the costs |
| A few big bets | One wrong call can sink the whole portfolio | Set a maximum share for any single holding |
| Sticking with what you know | Hidden concentration in one company or industry | List how much rides on your employer and your region |
| Crediting wins to skill | Taking more risk after a lucky streak | Compare your returns with a simple index fund |
Why does overconfidence make fraud more likely?#
Feeling sure that you would notice a scam can lower your guard. The SEC-commissioned report notes that in the worst-case outcome, an overconfident investor becomes a victim of investment fraud, such as a Ponzi scheme[1].
The 2024 survey data point the same way: among investors who feel highly knowledgeable, 51% were unable to identify the warning signs of fraud, which the report says suggests that overconfidence can put investors at risk[3]. Not every study finds a clear link — the FINRA Foundation study of older adults found no consistent effect of overconfidence on scam susceptibility[2] — so treat it as a risk factor, not a certainty. Learn the red flags of investment fraud whatever your level of confidence.
How can you keep your confidence in check?#
Write down why before you buy
Note your reasons and what would prove you wrong. Reread the note later; it shows whether your calls were good or just lucky.
Keep score honestly
Compare your results, after costs, with a plain index fund held over the same period. If you are not beating it, that is useful evidence about how much edge you really have.
Cap the size of any single bet
Decide in advance the most you will put into one stock or one idea, so a single mistake cannot sink the plan.
Slow down your trading
Set a rule, such as reviewing the portfolio on a fixed schedule, and avoid acting on headlines in between.
Test your knowledge, not your feelings
Take a free investor quiz or read a regulator's guide on a topic you think you know. Gaps you find are cheaper to learn about there than in the market.
What mistakes do beginners make?#
Treating a winning streak as proof of skill
A few good results can come from luck or a rising market. Compare your returns with a simple benchmark over several years before concluding anything.
Concentrating in what feels familiar
Knowing a company as a customer or employee is not the same as knowing its value. Keep any single holding to a size you could afford to lose.
Ignoring the cost of each trade
Spreads, fees and taxes are small per trade but add up. Total them for a year before deciding your trading adds value.
Assuming you would spot a scam
Survey data show many confident investors miss fraud warning signs. Verify every unsolicited offer, however obvious a scam seems from the outside.
What else do beginners ask?#
Is overconfidence the same as optimism?
No. Optimism is expecting good outcomes. Overconfidence is overrating your own knowledge or ability to predict. Researchers measure it as the gap between confidence and tested knowledge[2].
Do experienced investors suffer from overconfidence too?
Yes. The SEC-commissioned report describes overconfidence as common among investors, and links it to the susceptibility of otherwise sophisticated investors to fraud[1].
Is day trading a sign of overconfidence?
Not necessarily, but it raises the stakes. FINRA's day-trading disclosure warns that it can be extremely risky and generates substantial commissions even when the per-trade cost is low[8].
How can I tell if I'm overconfident?
Compare your expectations with evidence. Keep a record of your predictions and reasons, and compare your after-cost results with a simple index fund. A large gap between what you expected and what happened is the clearest sign.
What is the bottom line?#
Overconfidence is common: most investors in a large U.S. survey rated their knowledge highly, yet on average respondents answered fewer than half of a basic quiz correctly. The cost shows up as extra trading, concentrated bets and missed fraud warnings. You do not need to lose confidence to fix it — you need to test it, by writing down your reasons, capping position sizes and comparing your results with a plain benchmark.
Sources
Numbers in brackets in the text point here. Grade A = primary source (regulator, statistics agency, law or official document).
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