Anchoring bias is the tendency to let whatever you consider first drag your judgement toward it — usually a number, but not always — even when it is irrelevant, random, or obviously made up.
Named by Amos Tversky and Daniel Kahneman, who set out anchoring and adjustment as one of three core heuristics in their 1974 paper in Science.
// Where it sits
We estimate by starting somewhere and adjusting — and we reliably stop adjusting too early.
What it really means
The detail that makes the original anchoring experiment unforgettable is that the participants watched the number appear in front of them, as far as they knew by chance. Tversky and Kahneman spun a wheel of fortune — quietly rigged to stop on 10 or 65 — let it land, and then asked what percentage of African countries belonged to the UN. People who had just seen the wheel stop on 10 gave a median answer of 25%. People who had seen it stop on 65 said 45%.
Nobody thought the wheel knew anything about Africa. The anchor didn't need to be credible, relevant, or even plausible — it only needed to be first.
The mechanism is in the name Tversky and Kahneman gave it: anchoring and adjustment. Asked to estimate something uncertain, we start from whatever number is available and move away from it until the answer feels acceptable. The flaw isn't the starting point; it's that we stop adjusting far too early. Which is why the same paper's other demonstration works: given five seconds, people estimate 8×7×6×5×4×3×2×1 at around 2,250, and the identical digits ascending at 512. The real answer is 40,320, and the only thing that changed was which digit you saw first.
Where it comes from
Anchor is Old English ancor, from Latin ancora, from Greek ankyra; the psychological sense comes from Tversky and Kahneman's anchoring-and-adjustment account (1974). The image holds: the first figure drops an anchor, and your adjustment can only swing so far before the chain pulls tight.
Myths & misconceptions
Anchoring only works on people who don't know the subject.
Experts are anchored too, if only slightly. In a 2025 study, scientists assessing papers they had previously cited shifted their quality judgments a little with a random number printed on the questionnaire — while the real citation counts, the anchor you would expect to bite, did nothing.
The anchor has to be believable to work.
It doesn't. The original anchor came from a wheel of fortune spun in front of the participants, who had every reason to treat the result as chance — it was in fact rigged to stop on 10 or 65 — and it still moved the median estimate by 20 percentage points.
Compare & contrast
Anchoring vs the framing effect
Anchoring is about a reference point — usually a starting figure, and it pulls your estimate toward it. Framing is verbal — the same fact described as '90% survival' or '10% mortality' changes which option you pick. Anchoring shifts how much; framing shifts whether.
| // | Anchoring | Framing effect |
|---|---|---|
| Operates on | Numbers | Descriptions |
| Changes | Your estimate | Your choice |
| Needs relevance | No | No |
| Defence | Pre-commit a figure | Restate both ways |
How it connects
- Decoy Effectboth plant a reference point — one a number, one a whole option.
- Framing Effectthe verbal counterpart, from the same research programme.
Tell it apart
Questions people ask
- What is anchoring bias?
- Letting an initial number set the range you argue inside. A flat listed at £400,000 makes £385,000 feel like a win — even if comparable flats on the same street go for £350,000. The asking price was never evidence, but it became the reference point.
- Why does it work even with random numbers?
- Because we estimate by starting somewhere and adjusting, and the adjustment stops too soon. Participants watched a wheel of fortune land on 10 or 65 and still let it move their answers by 20 points — knowing it was random didn't help.
- How do you defend against it?
- Generate your own number before you see theirs, and write it down. Decide what a used car is worth from listings and its service history before opening the seller's ad. A figure you committed to in advance is much harder to reel in.