Cognitive load is the amount of mental effort a page asks for before someone can act.
On a product page, every extra option, block of text or competing button adds load, and once it builds up, shoppers delay, pick the default or leave.
Decision fatigue is the related idea that making many choices in a row wears down the quality of later choices.
The lab evidence for decision fatigue is weaker than its reputation, but A/B tests that cut unneeded choices on product pages often win.
This page sticks to two questions. What does the research actually support?
And what happened when stores in our test database removed decisions, or added them back? It is part of our psychology hub.
Decision fatigue: what the research shows, and what it doesn't
The idea comes from "ego depletion" research. In 1998, Roy Baumeister and three colleagues proposed in the Journal of Personality and Social Psychology that choices and acts of self-control draw on one limited resource that runs down with use.
"Decision fatigue" grew out of that model: after enough decisions, people get worse at making the next one.
The famous evidence has problems
The best-known example is the "hungry judge" study.
Danziger, Levav and Avnaim-Pesso (PNAS, 2011) looked at more than 1,000 parole rulings by eight Israeli judges.
Favorable rulings started at about 65% after a food break and fell, sometimes to nearly zero, before the next break.
The finding has been seriously challenged. Weinshall-Margel and Shapard (PNAS, 2011) pointed out that cases were not heard in random order.
Prisoners without a lawyer tended to come last in a session.
Glöckner (Judgment and Decision Making, 2016) ran simulations and showed that a judge who simply avoided starting long cases right before a break would produce a similar pattern, with no fatigue at all.
Ego depletion itself has also failed large replications.
A 23-lab preregistered replication with 2,141 participants (Hagger and colleagues, 2016) found an effect of d = 0.04, with a confidence interval that included zero.
A second 36-site test led by Kathleen Vohs (Psychological Science, 2021), with 3,531 participants, found d = 0.06, which was not significant.
So treat "decision fatigue" as a useful way to talk about effort, not as a proven law.
Nobody has shown that a shopper's willpower runs out after a set number of choices.
What A/B tests show about fewer decisions
The tests are clearer than the lab work, but they tell a narrower story.
Removing a decision that doesn't help the shopper often wins.
That says nothing about a "tank" running dry.
It shows that each choice on a product page has a cost, and that cost has to be paid back in value.
- Oliver Kenyon removed a 1/2/3-bag bundle selector from a travel bag brand's product page: one bag, one price, one button. Conversion rate rose 8.7%, revenue per visitor 7.8% and profit per visitor 6.7%, and average order value did not move. Most buyers only wanted one bag, so the selector added a decision without adding revenue.
- DRIP Agency cut New Shades' collection page to about a quarter of its products (75% fewer) and reported +14% revenue. The source gives only headline figures, with no sample size or significance.
- BliVakker.no removed 3 fields from a 17-field registration step and got 11% more form submissions. An "ultra-light" version that stripped out even more did not do as well, according to the source.
Choice reduction is not a one-way rule, though.
When MarketingExperiments removed the subscription-length dropdown from a subscription funnel and locked everyone into monthly billing, conversion fell about 40%.
That choice mattered to buyers. For how much choice is too much, see our page on the paradox of choice.
@oliverkenyon
DRIP Agency
MarketingExperimentsCognitive load theory in UX: designing product pages that are easy to process
Cognitive load theory comes from education research. John Sweller set it out in "Cognitive load during problem solving" (Cognitive Science, 1988).
Sweller argued that working memory is small, so teaching methods that waste it make learning slower.
The working-memory limit is real and well studied.
Nelson Cowan's 2001 review in Behavioral and Brain Sciences put the limit at about three to five chunks, lower than the "seven plus or minus two" often quoted from Miller.
Don't turn that into a design rule like "never show more than four options".
Shoppers can look back at the page, so they don't have to hold everything in their heads at once.
The kinds of load on a product page
Nielsen Norman Group's Kathryn Whitenton (2013) applied the theory to interfaces.
The article defines cognitive load as "the amount of mental resources that is required to operate the system" and separates two kinds that matter for design:
| Type | What it is | Product page example | What to do |
|---|---|---|---|
| Intrinsic load | The effort of taking in the information the shopper needs and keeping track of their goal | Comparing sizes, reading what's in the box, checking delivery dates | Keep it, but make it easy to scan and compare |
| Extraneous load | Processing that uses mental effort but doesn't help the shopper decide | Payment icon rows, badge bars, duplicate buttons, popups, options few people want | Remove it, move it lower, or tuck it away |
The same article gives three tips: avoid visual clutter, build on mental models people already have, and take work off the user with images, pre-filled information and smart defaults.
Defaults have their own literature, covered in our default effect page.
Related principles such as Hick's law are in UX laws.
Tests that cut extraneous load
- Dave Diederen hid the payment icons below the add-to-cart button: +9.77% conversion rate and +14.12% revenue per visitor. Dave's reading was that the icons pulled attention away from the button at the moment shoppers were thinking about shipping and guarantees.
- Dave Diederen also replaced variant dropdowns with visual selector blocks: +3.95% conversion rate and +3.79% revenue per visitor. A dropdown hides the options behind an extra tap, so shoppers have to open it and remember what's inside. See variant selectors for more tests.
- GoodwillFinds removed the shipping and authentication sections from its mobile product page and moved "More Like This" up: +5.16% Add to Bag clicks. The test ran for only 8 days.
- Blend Commerce grouped Jackson's sprawling product information into an accordion: +15.21% conversion rate.
When cutting load backfires
Hiding or removing content is not free. Blend Commerce ran the same accordion idea at Vegepod and lost overall: -8% revenue per visitor and -2% conversion rate.
Desktop gained 26% in revenue per visitor while mobile lost 28%.
Vegepod rolled the change out on desktop only.
Something that saves effort on one device can hide information shoppers need on another.
Clean Commit's stripped-back mobile layout raised average order value 4.0% but cut conversion rate 4.2%, and bounce rate rose 14.3%.
Greyson Clothiers removed visual collection filters and revenue fell 10.5%.
Filters add things to the screen, but they cut the work of finding a product.
Two tests by Conversion Fanatics, on the same store, show the balance.
Expanding only the key option groups on mobile lifted mobile conversions 36.6%.
An earlier version that expanded every option group led by more than 40% early on, then faded to about -4%.
Fewer taps helped. Putting everything on screen at once did not.
Sometimes adding a step lowers load, because it makes the decision easier to understand.
Dave Diederen redesigned a supplement bundle selector to ask who the product was for before showing supply options with per-day pricing.
Conversion rate fell 5.22%, but average order value rose 15.48% and revenue per visitor rose 9.45%.
The question wasn't "how many choices?" but "does each choice make sense to the shopper?"
@DaveDiederen@DaveDiederen
Conversion Fanatics
Blend Commerce
Clean CommitConversion FanaticsHow to test it on your own product page
- List every decision and element above the add-to-cart button. For each one, ask whether it helps the shopper choose or only asks for attention.
- Test one removal at a time when you can. That way you learn which element mattered.
- Report mobile and desktop separately. The Vegepod test shows the two can move in opposite directions.
- Measure revenue per visitor, not just conversion rate. Removing an upsell or bundle can raise conversion while lowering order value, or the other way round.
- Wait for a planned sample size. Early leads fade, as the Conversion Fanatics test showed.
For a wider checklist, see our product page design guide and layout and design tests.