Anchoring Bias
ES: Sesgo de Anclaje PT: Viés de Ancoragem
Excessive reliance on the first piece of information received. In trading you anchor to the entry price — "I will wait for it to come back" — to round numbers, or to analyst price targets, and lose the flexibility to update the thesis when new data arrives.
What Anchoring Bias Is
Anchoring bias is the cognitive tendency to rely excessively on the first piece of information received — the anchor — when making subsequent decisions. Tversky and Kahneman documented it in 1974 with a famous experiment: they asked whether Gandhi died before or after the age of 9, or before or after 140. The figure, obviously absurd in both cases, systematically shifted the estimates that followed. Anchors operate below conscious awareness and are hard to neutralise even when recognised.
In trading it appears in ten different forms, all of them destructive.
Anchoring to the entry price is the most common: "my cost is 50, I will wait for it to come back". Price is at 35, the fundamentals have deteriorated, but the trader refuses to accept the new reality. Anchoring to round numbers: 100 looks like a fair price and 99.87 looks odd, so people buy and sell at psychological levels for no fundamental reason.
Anchoring to an analyst’s price target: someone sets a target and the trader holds the position waiting for it, when those forecasts are right around half the time. Anchoring to the all-time high: "it was worth 300 and now 100, it has to be cheap", ignoring that the fundamentals may justify the fall. And its mirror image, anchoring to the all-time low: "it was at 20 and now 80, it cannot be worth that much".
Anchoring to the annual range makes a stock near its highs look expensive and near its lows look cheap, regardless of fundamentals. Anchoring to the initial valuation: "I bought at a P/E of 15 and it is now 25, it is expensive", when growth may have accelerated and merit a higher multiple.
Anchoring to the first headline colours every subsequent interpretation. Social anchoring means the first post you read about a stock conditions your view. And anchoring to the IPO price, which was a largely arbitrary figure and yet becomes the reference for whether something is cheap or expensive.
The Classic Experiments
Tversky and Kahneman’s original experiments in 1974 are devastatingly clear. In the wheel of fortune study, subjects spun a wheel and then estimated what percentage of UN countries were African: those who spun high numbers gave far higher estimates, even though the number was manifestly random. With anchors of 10% and 65%, the average estimates were 25% and 45% respectively: the same question, twenty points apart.
In the Gandhi age study, asking about 9 or about 140 produced median answers of 50 and 67 years. An identical factual question with radically different answers.
The neurological basis is what is known as insufficient adjustment: the brain starts from the anchor, adjusts partially and stops too soon, because minimising cognitive effort is efficient. The result is a systematically short correction.
Professionals are not immune. In a study with estate agents shown the same property with different asking prices, the "correct" appraisals correlated with the advertised price rather than the state of the property. The same happens in negotiation: the first offer anchors the final outcome, and anchoring low in a salary negotiation costs thousands.
In investing, research shows that analyst price targets are heavily anchored to the current price: their revisions correlate with price movements more than with changes in fundamentals, to the point that the forecasts predict their own future targets better than the stock’s performance.
The most uncomfortable finding is that anchoring appears to be automatic: studies that explicitly instruct subjects to ignore the anchor fail to eliminate the effect. It operates below awareness, which is why the only real defence is systematic processes that route around it.
How to Counter It
Fighting it requires ten systematic processes, because willpower is not enough.
The first is starting from fundamental value: before looking at the price, estimate fair value by discounted cash flow or by comparables, and only then compare. That turns the price into an input rather than an anchor.
The second is resetting the analysis every quarter by explicitly asking: "if I did not hold this position, would I buy it today at this price?". That question bypasses the cost-basis anchor entirely.
The third is updating targets on fundamentals rather than price movements. The fourth is distrusting other people’s price targets, notoriously imprecise and anchored to the current price. The fifth is reasoning in terms of portfolio weight: if this position is 5% of the total, what is the optimal weight today, regardless of what it cost?
The sixth is framing the opportunity cost: is there a better use for this capital? Comparing alternatives weakens attachment to what you already hold. The seventh is time-bounded positions, with a prior commitment to exit if the thesis does not materialise within a set period.
The eighth is the devil’s advocate: periodically arguing the opposite case, starting with "what if the current price is the correct one?". The ninth is analysis from scratch, evaluating the asset as though you had just discovered it, without knowing its price history. And the tenth is the sell-half rule when a position has appreciated substantially, which resets the anchor and prevents holding it through inertia.
Buffett applies it explicitly: his decisions start from a calculation of intrinsic value, and price only matters as a buy or sell trigger against that value. His formulation that the market offers different prices every day and you pick the ones that suit you is exactly an anti-anchor stance.
Practical Application
In daily trading, the antidote is organised into seven disciplines.
The pre-trade checklist requires four things: calculating value independently of the current price, setting the entry on the gap between value and price, placing the stop on fundamental or technical criteria and never on the cost basis, and setting the target by fair value or technical levels rather than round numbers.
The quarterly review of each position answers three questions: whether you would buy it today at this price, whether the fundamental thesis has changed since entry, and whether there is a better use for that capital.
Stop discipline requires fundamental triggers — "I exit if quarterly revenue falls 10%" — rather than references to the price paid. Target discipline, likewise: fair value, technical resistance or risk-reward, never "I bought at 50 and I exit at 60 because 20% sounds good".
Sizing must start from the portfolio’s current value, current volatility and current conviction, not from inherited assumptions. In processing news it helps to write the thesis before reading, and only then update it with the facts, consulting several sources so as not to anchor to the first headline.
In options, expiration acts as a natural antidote, because it prevents holding a position indefinitely. The risk appears when rolling losers, which prolongs commitment to the original thesis; the solution is setting an absolute maximum loss per position regardless of any willingness to roll. It also pays to choose strikes by delta or expected move rather than by round figures.
The underlying idea is that anchoring is about mental flexibility. Markets change, companies change and valuations change; whoever stays anchored to a past decision cannot adapt. Keynes summarised it: when the facts change, he changed his mind.
Common Trading Anchors and What to Replace Them With
The solution is always the same: swap an anchored trigger for a fundamental criterion.
| Type of anchor | The problem | Better alternative |
|---|---|---|
| "Waiting to get back to breakeven" | Compare current value against price | |
| Arbitrary decisions | Technical levels or cash-flow valuation | |
| They are anchored to the current price | Your own independent valuation | |
| A feeling that it is expensive | P/E relative to growth | |
| A feeling that it is cheap | Analysis of business quality | |
| An artificial reference | Current intrinsic value |
Frequently Asked Questions
How do I overcome anchoring to the price I paid?
A complementary exercise is imagining you have inherited a stranger’s portfolio and evaluating each position without knowing what it was bought for. The decisions that come out of that bypass the anchor entirely.
Tax introduces a legitimate nuance, because realising gains or losses has consequences, but the underlying logic holds: today’s decisions should respond to today’s facts, not yesterday’s prices.
Why do round numbers seem so important?
It is worth recognising them as market structure — they are information about where the orders are — but not using them as your own decision criterion. Fundamental values rarely coincide with round figures, and setting a target at one of them means accepting someone else’s anchor.
Are analyst price targets reliable?
As an alternative, lean on your own calculation by discounted cash flow, on comparables valuation and on analysis of the historical range of multiples, averaging several sources rather than anchoring to one.
A revealing tell: those targets are usually revised after price moves, which confirms they follow price rather than anticipate it.
Do options reduce anchoring?
But there are three routes by which the bias creeps in anyway. Rolling losers prolongs commitment to the original thesis. Exercising an in-the-money option converts the position into a shareholding that can be anchored. And strike selection is usually made on round figures — the 100 strike on a stock at 99 — rather than objective criteria.
The solution is setting absolute rules about when rolling is permitted and choosing strikes by delta or expected move.
How does Keynes’s attitude help?
That flexibility is institutionalised through four practices: reviewing the thesis quarterly, setting invalidation criteria in advance, acknowledging errors openly, and not holding losing positions out of an unwillingness to admit the mistake.
It is probably the most powerful anti-anchoring practice there is, and a characteristic trait of professional managers against amateurs.