Anchoring Bias: How First Numbers Distort Investment Decisions

Key Takeaways

• The first number you see in any financial context anchors every subsequent estimate, even when that number is arbitrary.
• Analyst price targets cluster around round numbers precisely because of anchoring, not fundamental analysis.
• Your purchase price is irrelevant to whether a stock is attractive today, re-anchor each decision on current fundamentals.
• The 52-week high effect persists because investors are slow to revise their expectations past an old price ceiling.

What It Is

Anchoring was formally described by Amos Tversky and Daniel Kahneman in their 1974 Science paper "Judgment under Uncertainty: Heuristics and Biases." They documented that people estimating unknown quantities use an initial value (an anchor) and then adjust from it, with the adjustment almost always too small. The final estimate stays biased toward the anchor even when the anchor is clearly arbitrary.

Their classic demonstration spun a wheel of fortune in front of participants, then asked them to estimate the percentage of African countries in the United Nations. When the wheel stopped at 10, median estimates were about 25 percent. When it stopped at 65, median estimates jumped to about 45 percent. The wheel had nothing to do with the question.

The Intuition

Estimation under uncertainty is hard, so the brain looks for a starting point. Any number that is available in the moment can fill that role, even one with no informational content. Once the anchor is in place, the mind treats it as the reasonable neighborhood and works outward in small steps.

In markets, anchors are everywhere. Your purchase price anchors your sense of fair value. A 52-week high anchors your sense of upside potential. A round-number price target anchors your expectations for next quarter. Historical valuation multiples anchor views about whether current multiples are cheap or expensive.

None of these anchors is information-free in the way a wheel of fortune is. Some of them carry real signal. The bias is using them more heavily than their signal justifies.

How It Works

Tversky and Kahneman described anchoring as a two-stage process: generate an initial estimate, then adjust. The adjustment step is typically insufficient, so the final estimate stays too close to the starting point. Later research has identified at least two mechanisms behind the effect.

Selective accessibility. The anchor activates memories and information consistent with it. If the anchor is 65 percent, examples of many African countries in the UN come to mind more readily. If the anchor is 10 percent, the opposite happens. The adjustment runs on an unbalanced evidence base.

Insufficient adjustment. Even when people know the anchor is arbitrary, the effort required to move away from it feels disproportionate. People stop adjusting as soon as the answer seems plausible, which usually means too close to the anchor.

In investing, academic studies such as George and Hwang on the 52-week high effect show that a stock trading near its 52-week high tends to outperform in the following months, partly because investors anchor to the old high and are slow to bid the price up through it.

Worked Example

You bought 100 shares of a company at 80. The stock is now at 60. New information emerges that justifies a fair value closer to 50.

An anchor-free analyst reviews the 50 estimate on its merits and sells. An investor anchored to the 80 purchase price sees the current price as depressed relative to a 80 world and holds, waiting for the price to "come back." The 80 anchor is not informative about current fair value, but it dominates the decision.

Flip the example. You bought at 80, the stock is now at 95, and new information argues fair value is closer to 120. An anchor-free analyst adds to the position. An investor anchored to a round-number price target of 100 takes profits at 95, capturing only a fraction of the upside.

Common Mistakes

1. Assuming sophisticated investors do not anchor. Studies of analyst price targets show systematic clustering around round numbers and around prior consensus, exactly the pattern predicted by anchoring. Seniority and credentials do not eliminate the bias.

2. Using purchase price as the reference for current decisions. Your cost basis is relevant for taxes. It has no direct bearing on whether the current price is attractive. Re-anchor each decision on current fundamentals, not the price you happened to pay.

3. Treating 52-week highs and lows as physical barriers. They are anchors, not support and resistance in any mechanical sense. They matter because enough participants treat them as meaningful, but they are not a standalone reason to trade.

4. Forgetting that charts themselves are anchors. The first price your eye sees on a chart (the leftmost bar, the most recent high) shapes your perception of everything else. Rotate timeframes and zoom levels to loosen the grip of a single visual anchor.

Frequently Asked Questions

What is anchoring bias in simple terms? Anchoring bias is when your brain gets stuck on the first number it sees and struggles to move away from it. In investing, that number is usually your purchase price, and it can stop you from making rational sell decisions even when the facts have changed.

How does anchoring bias affect investment decisions? It distorts both buy and sell decisions. Investors hold stocks waiting for the price to "come back" to the purchase price, and sell winners once they hit a round-number target, behaviors driven entirely by arbitrary anchors rather than current fundamentals.

What is a real-world example of anchoring bias? You bought a stock at 80. It now trades at 60 and new information argues fair value is closer to 50. An anchor-free analyst sells. An investor anchored to 80 sees the current price as depressed and holds, waiting for a return to a reference price that carries no informational content about the present.

How can investors reduce anchoring bias? Reframe each decision as "would I buy this today at the current price?" rather than "is this above or below what I paid?" Reset price targets quarterly using current fundamentals. Vary chart timeframes deliberately to loosen the grip of a single visual anchor on your perception of fair value.

How is anchoring bias different from the sunk cost fallacy? Anchoring bias is about the first number skewing all subsequent estimates, including your sense of fair value and upside potential. The sunk cost fallacy is about unrecoverable past spending influencing forward decisions. Your purchase price can function as both an anchor (distorting fair-value judgments) and a sunk cost (distorting the sell decision) simultaneously.

Sources

1. Tversky, A. & Kahneman, D. (1974). "Judgment under Uncertainty: Heuristics and Biases." Science 185(4157), 1124-1131. https://www.science.org/doi/10.1126/science.185.4157.1124
2. Corporate Finance Institute. "Anchoring Bias." https://corporatefinanceinstitute.com/resources/career-map/sell-side/capital-markets/anchoring-bias/
3. "Industry information and the 52-week high effect." https://gattonweb.uky.edu/faculty/lium/52weekhigh.pdf
4. The Decision Lab. "Anchoring Bias." https://thedecisionlab.com/biases/anchoring-bias

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.