Anchoring bias

Anchoring bias is the tendency to depend too heavily on an initial number or value when making estimates or decisions. That first figure — the “anchor” — becomes a disproportionate reference point, even when it is arbitrary or irrelevant, and subsequent adjustments away from it are typically insufficient.

The classic experiment

In 1974, Daniel Kahneman and Amos Tversky conducted a now-famous study. They asked subjects to estimate what percentage of African nations belong to the United Nations. Before answering, each subject spun a wheel that randomly landed on either 10 or 65. Those who saw 10 estimated an average of 25%. Those who saw 65 estimated an average of 45%. The wheel outcome had nothing to do with the question. Yet it anchored the answer.

This is the core of anchoring bias: when we are asked to estimate something uncertain, we tend to start with whatever number is salient (present, recent, or explicitly provided) and then adjust insufficiently away from it. The “correct” anchor is less important than the fact that some anchor is in play.

Why it happens

The mechanism appears to involve two stages. First, the anchor is unconsciously activated — your mind treats it as a starting point. Second, you make adjustments from that point, but the adjustments are too small. You move a little way away from the anchor and then stop, interpreting that adjusted figure as your best estimate.

The fact that the anchor can be random or explicitly irrelevant (like a roulette wheel) shows that anchoring operates at a pre-conscious level. You are not deliberately reasoning “the wheel said 10, so I’ll start there.” Your mind does it automatically.

Anchors are stickier when they are:

• Recently seen or mentioned
• Presented as a specific number rather than a round figure
• Framed as coming from an authority or expert
• Relevant to the judgment at hand, even if they should not be

Anchoring in financial markets

Anchoring drives some of the most consequential mistakes in investing.

IPO and initial prices. When a company goes public at a high price, investors often anchor to that initial offer price when forming expectations about where the stock “should” trade. If the price falls later, the anchor can make it feel cheap (“down 40% from its IPO price”), even if the IPO price was unjustifiably high to begin with.

Past highs. A stock that previously traded at $100 and now trades at $60 feels cheap to anchored investors, even if the fundamentals have deteriorated and $60 is too high. The past high becomes the reference point.

Round numbers and resistance levels. Stocks often cluster at round numbers (like $50, $100) because so many traders anchor to those psychologically salient levels.

Valuations. When you are told a company is worth $500 million, that figure anchors your estimate of what it actually is worth. Even professional valuators struggle to ignore that anchor, adjusting only partway to their own conclusions.

Distinguishing anchoring from related phenomena

Anchoring is not the same as status-quo bias, though they can compound each other. Status quo bias is the preference for things to stay as they are; anchoring is the distortion of estimates caused by an initial value. An investor can exhibit both: they like their current holdings (status quo bias) and they overestimate how much those holdings are worth because they paid a certain price for them (anchoring).

Anchoring also differs from availability heuristic. Availability bias relies on how easily examples come to mind; anchoring relies on a specific numerical starting point.

How to counteract anchoring

The fact that anchoring is largely unconscious makes it hard to eliminate by willpower alone. A few defenses work:

• Generate multiple anchors. Ask “what else could this be worth?” and deliberately construct alternative starting points. This forces conscious adjustment.
• Consider the source. If you realize the anchor came from an arbitrary source (a salesman’s opening bid, a round number, a headline), dismiss it explicitly and restart your estimate.
• Use a decision framework. Rather than adjusting from a number, build up your estimate from first principles — cash flows, earnings per share, market capitalization of comparables — and only then check it against any anchors you’ve encountered.
• Separate the past from the future. Consciously distinguish what a stock cost from what it is worth. The former is history; the latter is what matters.

For professionals, anchoring can actually be useful in reverse. Negotiators sometimes set an aggressive anchor knowing the other side will assume they will adjust. If you understand anchoring is operating, you can factor it into your strategy — but only if you are aware of it.

See also