Mark required and optional fields explicitly

When to use it

When checkout or signup fields carry no required or optional marking, or only some do, and clicks on the submit control run well above recorded form submissions.

How to run it

Mark every field both ways: an asterisk with a legend on required fields, and '(optional)' on optional field labels.

Why it works

Make the offer instantly understood

People who have to guess which fields are required guess wrong at the finish line. In Baymard's testing, 32% of users failed to complete a required field when forced to guess which unmarked fields were required.

Source: Baymard Institute