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A Sticky Buy Button on Long Product Pages: A/B Test

A fixed purchase CTA may make the buying action easier to reach on a long product page.

  • Product page
  • Purchase conversion rate (CR)

Control vs Variant

Absent on one side, present on the other.

Changed
Presence
Page
Product page
Difference
added

Hypothesis

This test measures the effect of presenting that CTA in a fixed position; its destination and the purchase flow remain the same in both arms.

How to run this test

Primary metric

Purchase conversion rate (CR)

Compare completed orders per assigned visitor with and without the fixed purchase CTA.

Other metrics

  • CTA click-through rateUse clicks as a diagnostic measure.
  • Add-to-cart rateCheck whether shoppers take the first purchase step.
  • Page exit rateCompare exits in the same session window.

What to check before and during the test

  • Sticky behaviorKeep the existing purchase control visible using one predefined sticky rule.
  • ActionIn both arms, the button must lead to the same point in the order flow and preserve product selection and validation.
  • Visitor historyReview new and returning visitors separately.
  • AppearanceKeep label, size, color and price information unchanged.
  • TriggerSet when the sticky behavior begins before launch.

Setup mistakes to avoid

  1. 1Do not make the sticky button large enough to cover much of the screen.
  2. 2Keep the button from covering important content.
  3. 3Do not change CTA wording, price or color in the same test.
  4. 4Avoid excessive shadows and animation.
  5. 5On mobile, keep the button from covering content when the keyboard is open.