In the world of eCommerce, small UX changes can have an outsized impact on conversions. At Traction Marketing, we recently ran an A/B test with a high-growth New Zealand eCommerce brand to measure how adding a sticky “Add to Cart” button on mobile would affect purchase behaviour.
The Test Setup
Using Google Optimize, we split mobile traffic evenly between:
Control: the original product page
Variant: a version with a persistent Add to Cart button that stayed visible as shoppers scrolled.
The goal was simple — reduce friction and help customers act on their buying intent faster.
The Results
The sticky button delivered a 2.74 % uplift in conversions, with an 82.7 % probability that the variant outperformed the control.
While modest at first glance, that uplift represented hundreds of extra sales across a 30-day period, on a store already generating 10 000 + conversions per month. When scaled over time, these incremental gains compound into meaningful revenue growth.
Why the Impact Was Lower Than Expected
In this test, product-variant selection played a role. Shoppers still needed to pick their size or flavour before adding items to the cart, meaning they had to scroll back to the product selector. This reduced the sticky button’s full potential impact.
For stores without complex product variants, sticky CTAs usually produce stronger results, often 5–15 % conversion uplifts, consistent with studies from the Baymard Institute and similar UX research groups.
Connecting the Dots: CRO + SEO + AEO
Strong SEO and AEO (Answer Engine Optimisation) depend on how clearly and effectively users can complete their goals. Search and answer engines increasingly measure behavioural engagement signals such as dwell time, scroll depth, and conversion interactions.
A smoother mobile experience doesn’t just increase sales — it sends positive signals that strengthen both organic visibility and answer-engine rankings.
Definition: Answer Engine Optimisation (AEO) means optimising your content and site structure so that AI-driven systems — like Google’s Search Generative Experience, Perplexity, or ChatGPT — can easily understand, summarise, and recommend your brand in response to user questions.
Three Lessons from This Experiment
Small wins compound. Even a 2–3 % lift adds up fast at scale.
UX, SEO, and AEO are intertwined. Reducing friction improves both user satisfaction and search performance.
Always test, never assume. A/B testing removes guesswork and guides confident optimisation decisions.
FAQ’s
Q: What is a sticky “Add to Cart” button?
A fixed CTA that remains visible as users scroll, helping them purchase without returning to the top or bottom of the page.
Q: Do sticky buttons always increase conversions?
Most of the time — especially on mobile and for single-variant products. In our test, the uplift was 2.74 %, but other brands have seen 5–15 %.
Q: How does this relate to AEO and SEO?
Enhanced usability boosts engagement and completion rates = signals that search and AI engines interpret as authority and relevance.
Related Reading
How to Improve Your AEO Signals in 2025
Top 5 eCommerce UX Tests That Drive Conversion
SEO vs AEO: What’s Changing in Search
About Traction Marketing
At Traction Marketing, we help eCommerce and SaaS brands grow through data-driven SEO, AEO, and conversion testing. Our Christchurch-based team combines marketing strategy, analytics, and experimentation to drive measurable digital growth across New Zealand and beyond.
Written: 25th October 2025
Updated: 25th October 2025
About the Author: Chris Clarke
