A stock trades at $50. You watched it briefly at $40 last month, thought about buying it, and did not. Now, at $50, you feel less inclined to buy than you would if you had first noticed it at $50. This intuition — that the earlier $40 makes the current $50 feel expensive — is anchoring, one of the most consistently documented cognitive biases in decision-making. Its effect on investment decisions is subtle, persistent, and almost impossible to argue away purely by understanding it.
The classic experiment
Kahneman and Tversky's original demonstrations of anchoring were simple. Subjects were asked to spin a wheel of fortune that produced a random number between 0 and 100. Then they were asked an unrelated question — for example, what percentage of African countries belong to the UN. The subjects who had just spun a low number produced systematically lower answers than those who had spun a high one. The random number, entirely irrelevant to the question, had anchored their answers.
The effect has been replicated in hundreds of studies with sophisticated professionals under high-stakes conditions. Real-estate agents given fictitious "list prices" for houses valued them at prices that correlated with the fictitious anchor, even when the agents insisted they had ignored the anchor. Experienced criminal judges given randomly-generated sentence "requests" produced final sentences that correlated with the random request.
Anchoring is not a beginner's mistake. It happens under expert conditions and cannot be turned off by knowing about it.
How it shows up in investing
The most common form is anchoring on cost basis. A stock you bought at $100 feels different from a stock you bought at $50, even if both are currently at $75. On the first stock you have a "loss"; on the second you have a "gain." The two mental categorisations produce different decisions about the same current position and the same current outlook.
The disposition effect — the tendency to sell winners early and hold losers too long — is anchoring plus loss aversion. Selling a "winner" locks in a gain relative to the anchor; selling a "loser" locks in a loss relative to the anchor. Investors take the pleasurable action (locking in gains) sooner than they should and defer the painful action (accepting losses) longer than they should.
Anchoring on past prices — beyond just cost basis
A stock you first watched at $30 feels differently at $50 than a stock you first watched at $50 does at $50. The initial anchor persists even if it was formed casually and even if the reasons for watching the stock originally are now irrelevant.
This affects entry decisions on stocks you have followed for a long time. A stock that has run from $30 to $60 while you watched but did not act may feel "expensive at $60" for reasons purely psychological — the anchor is your own history of watching, not any analytical judgment about current value.
The reverse also happens. A stock that has fallen from $100 to $50 may feel "cheap at $50" purely because of the recent higher anchor, even if $50 is objectively expensive relative to fundamentals.
Anchoring on analyst targets and forecasts
Published price targets serve as external anchors even for sophisticated investors. A stock trading at $75 with an "average analyst target" of $90 feels differently from the same stock trading at $75 with an average target of $70, even if the underlying fundamentals are identical.
This is one of the reasons published targets, upgrades, and downgrades move prices immediately and meaningfully — not because the target itself contains new information, but because it repositions the anchor around which market participants are evaluating the security.
Why understanding the bias does not remove it
The frustrating property of anchoring is that being aware of it provides only a modest defence. Studies in which subjects are explicitly warned about the anchoring effect and asked to disregard the anchor still find substantial anchoring in the results. The mechanism operates below the level of conscious deliberation.
What understanding does provide is the recognition that a strong intuition about "how expensive" or "how cheap" a stock feels may be tracking your anchor rather than any objective valuation input. That recognition is a partial defence — enough, sometimes, to prompt the extra analytical work that overrides the intuition.
Practices that measurably reduce anchoring
Zero-base the valuation. Ask "if I first heard of this company today, at this price, with these fundamentals, what would I think of it?" Answering that question honestly, in writing, forces some of the anchor's influence out of the analysis. It does not eliminate the effect but it reduces it.
Set exit rules that are not price-anchored. "I will sell if my thesis is invalidated by fundamentals" is a rule not anchored to price. "I will sell if the stock drops 20%" is a rule anchored to your entry price. The first is a discipline; the second is anchoring dressed as one.
Do not check the cost basis before making decisions. Some brokerage platforms allow you to hide unrealised P&L per position. Using this reduces the anchoring effect on decisions about existing positions — you are evaluating what you have on its current merits rather than as a "winner" or "loser" relative to your entry.
The rule to internalise
Every price you have ever noticed for a security you follow is a partial anchor. The anchor influences every decision you make about the security, whether you notice it or not. You cannot eliminate the effect through understanding, but you can build practices that partially override it. The investors who compound wealth over long horizons are almost never the ones with the sharpest intuitions; they are the ones with the most disciplined practices that neutralise the intuitions that would otherwise sabotage them.
Educational content only. Not investment advice.