Planning fallacy

We underestimate how long our own tasks will take, even when similar tasks ran late before.

Buehler, Griffin & Ross (1994), Exploring the "planning fallacy": Why people underestimate their task completion times.

≡

What is Planning fallacy?

Planning fallacy is a behavioural bias (judgement family): we underestimate how long our own tasks will take, even when similar tasks ran late before. Onboarding, setup and "finish your profile" flows feel quicker than they are, so people start and stall. Nudgeswipe rates the evidence as strong. Source: Buehler, Griffin & Ross (1994), Exploring the "planning fallacy": Why people underestimate their task completion times.

▮▮

The research

Onboarding, setup and "finish your profile" flows feel quicker than they are, so people start and stall.

● Strong evidence (provisional)

Provisional rating: we cite only the original paper so far. It stays provisional until a replication or meta-analysis is added.

Source: doi.org/10.1037/0022-3514.67.3.366

✓

Key takeaways

Honest nudge
Show honest time estimates ("about 6 minutes") and save progress.
Dark-pattern line
Promising "60 seconds" for a flow that takes far longer, so people are already invested when they find out.

Use it

Apply this with your agent

The prompt carries this bias, its evidence rating and the honest-vs-dark line.

You are helping me apply a behavioural bias ethically in my product.

Bias: Planning fallacy (Judgement, strong evidence): We underestimate how long our own tasks will take, even when similar tasks ran late before.
How it works: Onboarding, setup and "finish your profile" flows feel quicker than they are, so people start and stall.
Source: Buehler, Griffin & Ross (1994), Exploring the "planning fallacy": Why people underestimate their task completion times. https://doi.org/10.1037/0022-3514.67.3.366
Honest use: Show honest time estimates ("about 6 minutes") and save progress.
Dark-pattern line: Promising "60 seconds" for a flow that takes far longer, so people are already invested when they find out.
Page: https://nudgeswipe.com/biases/planning-fallacy/ (JSON: https://nudgeswipe.com/api/biases/planning-fallacy.json)

Rules: say a brand "uses" a tactic, never that it "worked"; outcomes are not public unless the company published them; no invented uplift estimates; flag mixed evidence. Honest nudge = true, visible, easy to reverse, and in the user's interest. Dark pattern = hides costs, fakes scarcity or popularity, shames, or makes leaving harder than joining. Quote company-published results as "X reports", with the source link, and don’t generalise them. Don’t cite retracted or failed-to-replicate studies as support (e.g. Ariely & Wertenbroch 2002). Don’t state study figures unless they’re on this page or in a source you can link. If an idea crosses the line, link the matching deceptive.design pattern.

Tasks:
1. Ask me for my product, the flow and the goal.
2. Audit where planning fallacy already shapes that flow, for better or worse.
3. Propose 2-3 ethical experiments: hypothesis, variant, primary metric, guardrail metric.
4. Flag dark-pattern risks. The rating is provisional: no replication or meta-analysis is cited yet.

Open in ChatGPT Open in Claude Open in Grok Open in Cursor

ChatGPT, Claude, Grok and Cursor open with the prompt filled in (it is also copied, in case the prefill doesn't load). Gemini and Codex don't support prefilled links, so the prompt is copied and the app opens; paste it in.

Frequently asked questions

What is Planning fallacy?

Planning fallacy is a behavioural bias: we underestimate how long our own tasks will take, even when similar tasks ran late before.

How does Planning fallacy work?

Onboarding, setup and "finish your profile" flows feel quicker than they are, so people start and stall.

How strong is the evidence for Planning fallacy?

Nudgeswipe rates it strong evidence (provisional). Original source: Buehler, Griffin & Ross (1994), Exploring the "planning fallacy": Why people underestimate their task completion times.

How can you use Planning fallacy honestly?

Show honest time estimates ("about 6 minutes") and save progress.

When does Planning fallacy become a dark pattern?

Promising "60 seconds" for a flow that takes far longer, so people are already invested when they find out.

In the wild

No teardown yet

We haven't captured a real product or email using planning fallacy yet. Seen one? Use the prompt above to audit your own flow, or browse all teardowns.

5 new nudges, every Friday

Five real product and marketing moments, the psychology behind each, and one thing to try. Weekly issues start soon. Your email is stored with our email provider (Resend) and used only for this newsletter.