Does website speed affect conversion rate?

Key takeaways

Yes, website speed affects conversion rate, especially on mobile. Faster pages keep more visitors and give them less reason to give up before acting. Published case studies show clear effects, but speed is a threshold, not a race: once key pages load quickly on mobile data, clarity and proof matter far more than shaving off further milliseconds.

• 8% more sales followed a 31% improvement in LCP in a Vodafone test.
• The BBC lost an extra 10% of users for every additional second of load time.
• Aim for 'good' Core Web Vitals on mobile for your top landing pages.
• Beyond that threshold, content usually beats further speed work.

How does website speed affect conversion?

Speed affects conversion by changing how many visitors stay long enough to act, and how easy acting feels. Slow pages lose visitors before the content appears. Slow responses to taps make forms and menus feel broken. Both cut the number of people who reach the enquiry or checkout.

• The difference between a good website and a high-converting website

What does the evidence show?

Google's web.dev publishes case studies linking speed to business results. Vodafone ran a controlled test where a 31% improvement in Largest Contentful Paint (LCP) increased sales by 8%. web.dev also reports that the BBC found it lost an additional 10% of users for every extra second its site took to load.

These are large sites with enough traffic to measure small effects. The direction applies to small sites too, but the size of the effect will differ.

• Core Web Vitals for business websites

How fast is fast enough?

Fast enough means passing Google's Core Web Vitals thresholds on mobile for the pages that bring enquiries: LCP within 2.5 seconds, Interaction to Next Paint (INP) within 200 milliseconds, and Cumulative Layout Shift (CLS) below 0.1. Test in PageSpeed Insights using field data where available.

• How fast a business website should load

Which speed fixes are worth paying for?

Prioritise fixes that affect the first screen of your top landing pages on mobile. These usually give the biggest improvement for the least cost.

• Compress and correctly size images, especially the hero image.
• Remove or replace video headers on mobile.
• Cut unused plugins, scripts and tracking tags.
• Use good hosting with caching and a content delivery network.
• Load chat widgets and pop-ups after the main content.

• Optimise website images for speed and search
• Slow website: fix it or rebuild it?
• Does video on a website increase enquiries?

When does more speed stop helping?

Once pages pass Core Web Vitals comfortably, further speed work gives smaller returns than fixing clarity, proof and the enquiry route. A page that loads in 1.2 seconds with a vague headline will convert worse than one that loads in 2 seconds and answers the buyer. Speed removes a barrier. It does not persuade.

• Website conversion myths that waste budget

What does this look like in practice?

A UK garden centre's homepage took several seconds to show anything on mobile because of an autoplay video and a large slider. We replaced both with a single compressed image and the week's offers as text. Mobile engagement rose, and click-and-collect orders from mobile improved over the following weeks. The design barely changed. The first screen simply arrived sooner.

• See client work
• Website Design & Development for UK businesses

Speed and conversion checklist

• Test top landing pages in PageSpeed Insights on mobile.
• Fix the hero image and any video header first.
• Remove unused plugins, scripts and tags.
• Delay chat widgets and pop-ups.
• Aim to pass Core Web Vitals, then move on to content.
• Re-test after every significant site change.

Next step

Speed is worth fixing until it stops being a barrier. We will tell you whether your site is past that point or whether speed is still costing you enquiries.