What it is
Cognitive load is the mental effort a task demands. The idea comes from learning research: working memory is limited, and tasks that use more of it leave less capacity for anything else (Sweller, 1988).
Usability research applies the same idea to interfaces: every bit of reading, remembering and decoding uses capacity the visitor would rather spend on the decision (Nielsen Norman Group).
How strong is the evidence?
Moderate. That working memory is limited is well established. Applying cognitive load theory to websites is an extrapolation from learning research and usability studies, not a set of controlled conversion experiments. Use it to find problems, then test the fixes.
How it shows up on a page
Two kinds of effort:
- Effort the task needs. Choosing a plan, entering an address. You can make it easier, but not remove it.
- Effort the design adds. Clutter, jargon, inconsistent layouts, unexplained fees, having to remember a code from the previous page. This is the effort to cut.
Examples
Ecommerce
- A checkout that asks for the same address twice.
- Delivery options with names like “Standard Plus” and no dates.
- A product page where size, colour and stock are spread across three places.
- Helps: autofill, one clear delivery date per option, the key decision information next to the button.
SaaS
- A sign-up form with 12 fields before the user sees any value.
- Feature names that only make sense inside the company.
- Helps: ask only what’s needed now, use the customer’s words for features, show a short example of the result.
Ethics and accessibility
Low ethical risk, and a strong accessibility overlap: clear labels, consistent navigation and helpful error messages are WCAG requirements that also reduce load for everyone (WCAG 2.2). The one trap: “simplifying” by hiding information people need, like fees or contract terms. That’s not less effort; it’s a later surprise.
How to test it
- Hypothesis: “Because recordings show shoppers scrolling back to check delivery dates, we believe showing the date inside each delivery option will increase completed checkouts, because shoppers won’t need to remember or recheck it.”
- Primary metric: completion of the step or the whole journey.
- Secondary signals: time to complete, error rate, back-navigation.
- Guardrails: order value and support contacts.
Related: choice overload and checkout optimization.