What Is a Nudge?
Written by Paweł Raja, PhD · Published
Definition
A nudge is a change in how a choice is presented — the default, the order of options, the framing or the information shown alongside it — that predictably changes what people do without forbidding any option or significantly changing their economic incentives.
The term comes from Nudge (2008) by economist Richard Thaler and legal scholar Cass Sunstein, who define a nudge as:
“any aspect of the choice architecture that alters people's behavior in a predictable way without forbidding any options or significantly changing their economic incentives. To count as a mere nudge, the intervention must be easy and cheap to avoid. Nudges are not mandates.”
Their shorthand: putting fruit at eye level counts as a nudge; banning junk food does not. The idea rests on behavioral economics. People rely on defaults, are swayed by how options are framed and follow what others do, so the way a choice is presented (its choice architecture) changes what they pick even when the options stay the same.
Nudge vs. mandate vs. incentive
| Tool | What changes | Options | Example |
|---|---|---|---|
| Nudge | How the choice is presented | All kept, at the same cost; easy to opt out | Enrolling employees in a pension plan by default |
| Mandate or ban | Which options are allowed | Some removed | Banning junk food in school cafeterias |
| Incentive | What the options cost | All kept, at new prices | A tax on sugary drinks; a savings subsidy |
Types of nudges
Researchers commonly sort nudges into three families, the classification used by the largest meta-analysis of nudging (Mertens et al., 2022):
Decision structure
Changes the options themselves or how they are arranged: which option is the default, how many options there are, what order they appear in, and how much effort each one takes.
Defaults (opt-out instead of opt-in) · Number of options · Decoy options
Decision information
Changes what people see when they choose, without changing the options: describing outcomes differently, making a feature more visible, or showing what other people do.
Social norms ("most people pay on time") · Framing · Making costs or benefits salient
Decision assistance
Helps people follow through on what they already intend: reminders, and commitment devices that let them bind their future selves.
Commitment devices against present bias · Reducing the pull of the status quo
Nudge examples, with results
Field and lab studies from our findings database, each with its study design and the result its authors report:
- Social-Norm Tax Reminder Letters: The HMRC Natural Field Experiments — Taxpayers paying within 23 days (Experiment Two): Standard reminder letter 33.6% → Letter + local & debt norm 38.6% (+5.0 pts) (Natural field experiment)
- Johnson & Goldstein Organ Donation Defaults: Opt-In vs. Opt-Out — Respondents agreeing to be organ donors (online experiment): Opt-in default 42% → Opt-out default 82% (+40.0 pts) (Online experiment)
- Opower Home Energy Reports: Neighbor Comparisons Cut Energy Use by 2% — Household energy use relative to the randomized control group: Households receiving reports: −2.0% vs. control households without reports (Natural field experiment)
- Save More Tomorrow (SMarT): Committing Future Pay Raises to Retirement Saving — Average saving rate of SMarT participants (% of pay): Before joining SMarT 3.5% → After four pay raises (40 months) 13.6% (+10.1 pts) (Before–after (participants))
- Overcoming Algorithm Aversion: Letting People Slightly Modify an Algorithm's Forecasts — Participants choosing to use the algorithm's forecasts (Study 1): Algorithm could not be changed 32% → Could adjust each forecast by up to 10 percentiles 76% (+44.0 pts) (Lab experiment)
More detail on each: nudge examples that worked and the full findings database.
Do nudges work?
A 2022 meta-analysis in PNAS (Mertens et al.) pooled more than 200 studies and reported a small-to-medium average effect of choice-architecture interventions (Cohen's d ≈ 0.43). Decision-structure nudges such as defaults were the most effective family. Other researchers challenged that average as inflated by publication bias.
The most complete real-world test comes from DellaVigna and Linos (2022), who analysed all 126 randomized trials run by two US government nudge units, covering over 23 million people. The average nudge raised take-up by about 1.4 percentage points, against roughly 8.7 points in published academic studies. Most of the gap is explained by publication bias and by academic trials being smaller and using stronger interventions.
The practical reading is that nudges are usually small but cheap, which is why they can still be cost-effective at scale. Defaults are reliably powerful, many information-only nudges are modest, and any nudge should be tested in its own context rather than assumed to work.
Read the summaries of RCTs to Scale and The Effectiveness of Nudging.
Ethics, criticism and sludge
Autonomy and manipulation. Critics worry that steering choices, even toward good outcomes, bypasses people's reasoning. Thaler and Sunstein's answer, set out in 'Libertarian Paternalism' (2003), is that neutral design does not exist: some option has to come first and something has to happen if a person does nothing, so designers might as well choose arrangements that help people, while keeping opting out easy.
Transparency. A nudge that only works when it is hidden is hard to defend. The usual standard is that a nudge should still be acceptable once people know about it, and that overriding it should take one simple step.
Sludge. The same tools can be turned against people. Thaler (2018) calls this sludge: friction that makes it harder to do what is in your interest, such as cancellation processes far more tedious than signing up or rebates that require paperwork few people finish.
See the summary of Libertarian Paternalism (Thaler & Sunstein, 2003) for the original argument.
Nudges: frequently asked questions
What does nudge mean?
In behavioral economics, a nudge is any change in how a choice is presented that predictably changes behavior without banning options or significantly changing financial incentives. Thaler and Sunstein, who popularised the term in their 2008 book Nudge, add that a nudge must be easy and cheap to avoid: nudges are not mandates.
What is an example of a nudge?
Thaler and Sunstein's own example: putting fruit at eye level in a cafeteria counts as a nudge, while banning junk food does not. Other well-studied nudges include automatic enrollment in pension plans (a default people can opt out of), and tax letters telling late payers that most people in their area pay on time (a social norm).
Who created nudge theory?
Economist Richard Thaler and legal scholar Cass Sunstein, in the 2008 book Nudge: Improving Decisions About Health, Wealth, and Happiness, building on their 2003 paper 'Libertarian Paternalism'. Thaler received the Nobel Memorial Prize in Economic Sciences in 2017 for his contributions to behavioral economics.
What is the difference between a nudge and a mandate or an incentive?
A mandate or ban removes options; an incentive such as a tax or a subsidy changes what the options cost. A nudge does neither: every option stays available at the same price, and only the way the choice is presented changes, for example which option is pre-selected.
Do nudges actually work?
Often, but usually by less than headline studies suggest. Across all 126 trials run by two US government nudge units, the average nudge raised take-up by about 1.4 percentage points, roughly a sixth of the average in published academic studies (DellaVigna & Linos, 2022). Defaults are the most reliably powerful type; many information-only nudges have small effects.
What is choice architecture?
Choice architecture is the design of the environment in which people make decisions: which options exist, how they are ordered and described, and what happens by default. Anyone who designs a form, a menu, a website or a benefits package is a choice architect, whether they mean to be or not, so there is no neutral way to present a choice.
Are nudges ethical?
Proponents argue that because some choice architecture is unavoidable, it should be designed to help people, provided options stay open and opting out is easy. Critics raise concerns about manipulation and autonomy. A common test is transparency: a nudge should still be acceptable if people know about it.
What is sludge in behavioral economics?
Sludge is the opposite of a helpful nudge: friction that makes it harder for people to act in their own interest, such as long cancellation processes or paperwork-heavy rebates. Richard Thaler named it in a 2018 Science essay, 'Nudge, not sludge'.
Sources
- Thaler, R. H., & Sunstein, C. R. (2008). Nudge: Improving decisions about health, wealth, and happiness. Yale University Press. [summary]
- Thaler, R. H., & Sunstein, C. R. (2003). Libertarian paternalism. American Economic Review, 93(2), 175–179. [summary]
- Mertens, S., Herberz, M., Hahnel, U. J. J., & Brosch, T. (2022). The effectiveness of nudging. PNAS, 119(1), e2107346118. [summary]
- DellaVigna, S., & Linos, E. (2022). RCTs to scale: Comprehensive evidence from two nudge units. Econometrica, 90(1), 81–116. [summary]
- Thaler, R. H. (2018). Nudge, not sludge. Science, 361(6401), 431. doi:10.1126/science.aau9241
Cite this page
Raja, P. (Ed.). (2026, 18 Oct 2026). What Is a Nudge? Meaning, Types & Examples. Behavioral Economics Lab. https://www.behavioraleconomicslab.com/what-is-a-nudge