Biases › Price
Price
Zero-price effect
Free feels different from cheap, not just cheaper.
'Free' is treated as more than just a lower price.
Shampanier, Mazar & Ariely (2007), Zero as a special price.
What is Zero-price effect?
Zero-price effect is a behavioural bias (price family): 'Free' is treated as more than just a lower price. Moving a price to zero shifts choice more than an equal cut elsewhere. Nudgeswipe rates the evidence as mixed. Source: Shampanier, Mazar & Ariely (2007), Zero as a special price.
The original study
Shampanier, Mazar & Ariely (2007), Zero as a special price.
- Method
- People chose between a Lindt truffle and a Hershey's Kiss at different prices, including when both prices were cut by the same 1 cent so the Kiss became free.
- What it found
- With prices of 15¢ (truffle) and 1¢ (Kiss), 27% of those choosing a chocolate took the Kiss. When both were cut by 1¢ (14¢ and free), the Kiss share rose to 69% of those who chose a chocolate (people choosing nothing were excluded). That is far more than standard cost-benefit models predict.
The research
Moving a price to zero shifts choice more than an equal cut elsewhere. Evidence comes from a small number of mostly lab studies.
● Mixed evidence
Source: doi.org/10.1287/mksc.1060.0254
Mixed evidence: effect sizes vary widely across studies. Treat it as something to test, not a law.
Key takeaways
- Honest nudge
Make 'free' real and say what happens when it ends.
Example: Mailchimp preselects a free trial of its Standard plan → - Dark-pattern line
Free trials that roll into paid plans without clear notice. deceptive.design →
Grey-area example: PureGym pairs a £0 joining fee with "ends Monday" →
Use it
Apply this with your agent
The prompt carries this bias, its evidence rating and the honest-vs-dark line.
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 Zero-price effect?
Zero-price effect is a behavioural bias: 'Free' is treated as more than just a lower price.
How does Zero-price effect work?
Moving a price to zero shifts choice more than an equal cut elsewhere. Evidence comes from a small number of mostly lab studies.
How strong is the evidence for Zero-price effect?
Nudgeswipe rates it mixed evidence. Original source: Shampanier, Mazar & Ariely (2007), Zero as a special price.
How can you use Zero-price effect honestly?
Make 'free' real and say what happens when it ends.
When does Zero-price effect become a dark pattern?
Free trials that roll into paid plans without clear notice.
Which brands use Zero-price effect?
Nudgeswipe has 28 teardowns of brands using it, including Mailchimp, Spotify, PureGym, Klaviyo, Linear. Whether it lifted their results is not public unless a teardown cites it.
In the wild
28 real examples
Mailchimp preselects a free trial of its Standard plan
Mailchimp · Pricing · $ as captured
Spotify leads with "£0" and spells out the price after
Spotify · Pricing · £ as captured
PureGym pairs a £0 joining fee with "ends Monday"
PureGym · Homepage banner · £ as captured
Klaviyo leads with 'Start with a free plan' and lists the caps
Klaviyo · Pricing page · $ as captured
Linear's pricing: 'Free for everyone' and 40,000 companies
Linear · Pricing page · $ as captured
Gymshark rotates five offers in one top banner
Gymshark · Homepage banner · £ as captured
Amazon frames the Prime trial as "30 days, on us"
Amazon · Paywall / trial
YouTube Premium promises a reminder 7 days before the free month ends
YouTube · Paywall / trial · $ as captured
Canva puts a generous free plan first and a "Save from 16%" yearly toggle on top
Canva · Pricing page · $ as captured
Grammarly says "$0 payment today" and promises a reminder 2 days before the trial ends
Grammarly · Pricing page · $ as captured
Trello makes the free plan concrete: "Free for up to 10 collaborators"
Trello · Pricing page · $ as captured
Squarespace stacks an undated 20% code on top of a free trial
Squarespace · Pricing page
ChatGPT puts an $8 step between Free and $20 Plus
ChatGPT · Pricing page · $ as captured
Deliveroo Plus sells a subscription as "free delivery"
Deliveroo · Subscription page · £ as captured
Asana labels its entry plan "Free forever" for one or two people
Asana · Pricing page · $ as captured
GitHub Copilot labels its $100 Max plan "BEST VALUE" by multiples of Pro credits
GitHub Copilot · Pricing page · $ as captured
Google sells Gemini plans as "2x" and "4x" the free usage
Google Gemini · Pricing page · $ as captured
Lovable frames the yearly plan as "2 months free" and starts with "No credit card needed"
Lovable · Pricing page · $ as captured
The Times sells a puzzles-only side door: "£1 for your first 3 months"
The Times · Subscribe page · £ as captured
Peloton App: "Try 30 days free", then from £12.99 a month
Peloton · App page · £ as captured
LinkedIn Premium splits visitors into "Advance your career" or "Grow your business" before any price
LinkedIn Premium · Premium landing page
Uber One sells a £4.99 membership on "£0 Delivery Fee" and credits paid back as a percentage
Uber One · Membership page · £ as captured
Moonpig pairs a "FREE CARD with any bouquet" with 30% off the first card
Moonpig · Homepage
v0 gives "$2 of free daily credits on login" and a one-time $5 for new users
v0 (Vercel) · Pricing page · $ as captured
Trading 212 shows a sample "Your earnings" widget from share lending, under a risk warning
Trading 212 · Homepage
Freetrade repeats "FREE" three times and leans on FCA and IG Group
Freetrade · Homepage
✅ 3 Free Songs ✅ Unlimited Sound Effects ✅ Licensed Forever
Musicbed values its free trial at $177 and explains the renewal
Musicbed · Email · $ as captured
Don't miss your FREE Eye Shadow Triple
Jane Iredale gives a $38 'value' gift with a $100 order
Jane Iredale · Email · $ as captured
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