---
title: "Deloitte: 0.1s faster mobile speed lifted retail conversion 8.4%"
url: https://seomadman.com/studies/page-speed-conversion-rate-impact
section: studies
published: 2026-08-08T00:00:00.000Z
modified: 2026-08-08T00:00:00.000Z
author: Adam Hafez
topics: ["Technical SEO"]
---

# Deloitte: 0.1s faster mobile speed lifted retail conversion 8.4%

## The short answer

Deloitte and Fifty-Five tested 37 retail, travel, luxury and lead-generation brand sites over four weeks in late 2019. A 0.1 second mobile speed improvement lifted retail conversion rate by 8.4% and average order value by 9.2%, while travel conversion rose 10.1%. Shopify's newer data found a similar pattern: 100 milliseconds slower load costs roughly 3.5% conversion.

## Key takeaways

- Deloitte and data partner Fifty-Five tested 37 retail, travel, luxury and lead-generation brand sites across Europe and the US over four weeks in October and November 2019.
- A 0.1 second mobile speed improvement was linked to an 8.4% lift in retail conversion rate and a 9.2% lift in average order value.
- Travel conversion rate rose 10.1% for the same 0.1 second mobile speed improvement, though travel average order value moved only 1.9%.
- Shopify's own 2026 analysis of Core Web Vitals data found that every 100 milliseconds of slower load time correlates with roughly 3.5% lower conversion.
- Deloitte's own report calls the finding a correlation observed across 37 already-live sites, not a controlled experiment, and notes that desktop data showed contradicting results.

Deloitte and Google-commissioned research firm Fifty-Five spent four weeks in late 2019 measuring
what a fraction of a second of mobile page speed is worth to 37 brand sites. Their headline number,
an 8.4% lift in retail conversion rate for a 0.1 second improvement, still gets quoted constantly.
Shopify has since published its own, more recent read on the same relationship. Here is what each
study actually measured, and where the two claims are Deloitte's and Shopify's findings, not ours.

## What Deloitte actually measured

**Thirty-seven brands, one four-week window.** Fifty-Five recruited over 70 retail, travel, luxury
and lead-generation brands across Europe and the US, and 37 passed its analytics, technical and
qualitative audits. From 28 October to 24 November 2019, it collected mobile site speed data
through Google Lighthouse and combined it with each brand's own web analytics: page views, bounce
rate, funnel progression, conversion rate and average order value.

**A regression model, not a controlled experiment.** Deloitte and Fifty-Five built a logarithmic
regression model to correlate four key mobile speed metrics with each site's KPIs, requiring at
least 95% statistical significance before a result was reported. Speed fluctuations were natural,
arising from each site's own performance work and traffic conditions, never artificially induced.
The published 0.1 second figure is the combined, cumulative effect of all four speed metrics
moving together, not one isolated change.

**Different verticals, different KPIs.** Retail and travel counted a completed transaction as
conversion. Luxury counted an add-to-basket or "contact us" click. Lead generation counted a
completed form. Retail conversion rose 8.4% and average order value rose 9.2%; travel conversion
rose 10.1% with a smaller 1.9% average order value gain; luxury page views per session rose 8%;
lead-generation informational pages saw an 8.3% bounce rate improvement.

## Why a correlation study is not a universal speed rule

**This measures sites that were already live and already changing.** Deloitte's own limitations
section is explicit: the 37 sites were "aggregated by vertical," which "may not fully reflect an
individual site's product offering, design, or seasonality." The study found a correlation between
naturally occurring speed changes and business metrics on sites that were already fast enough to be
running production ecommerce, not a controlled test of speed at every point on the scale.

**It does not extend to desktop, or to every speed range.** Deloitte says it looked for the same
correlation on desktop and "found a lot of contradicting parameters," attributing that to desktop
users being less sensitive to load time than mobile users. Nothing in the study implies a
0.1 second gain is worth the same 8.4% at every starting speed; a site already loading in under a
second and one loading in eight seconds are not shown to behave the same way for the same
improvement.

**Shopify's newer figure is a similar shape of claim, not a replication.** Shopify's enterprise
blog reports that across actively selling Shopify stores, every 100 milliseconds of slower load
correlates with roughly 3.5% lower conversion, based on 28 days of Largest Contentful Paint data
from around the turn of 2026. It also found stores with a 2.5 second LCP converting roughly 30%
worse than stores at 1.5 seconds. Different platform, different metric, same broad conclusion:
mobile speed and conversion move together, and the relationship looks steep at the low-millisecond
end most publishers actually operate in.

## Why we care

**The direction is well established; the exact multiplier is not portable.** Two independent
studies, six years apart and built on different site populations, both find meaningful conversion
sensitivity to small mobile speed changes. That is a solid reason to treat Core Web Vitals work as
revenue work, not just a ranking checkbox.

**Quote the vertical, not just the headline number.** "0.1 second equals 8.4% more conversions" is
true only for Deloitte's retail sample in 2019. Travel, luxury and lead-generation sites in the
same study moved by different amounts on different metrics, and neither study claims the effect is
linear at every speed level. Cite the study, the vertical and the metric together, or don't cite the
number at all.

## Frequently asked questions

### How many sites did Deloitte actually study?

37. Fifty-Five approached over 70 retail, travel, luxury and lead-generation brands across Europe and the US, and 37 qualified after analytics, technical and qualitative audits. Deloitte's own report says results "may not fully reflect the internet as a whole" for that reason.

### Does the 8.4% figure apply to every industry?

No. Deloitte broke results out by vertical. Retail conversion rose 8.4% and average order value rose 9.2%. Travel conversion rose 10.1% but average order value rose only 1.9%. Luxury and lead-generation sites did not use conversion rate as their KPI at all; Deloitte tracked page views per session and form completions instead.

## Sources

1. [Milliseconds Make Millions](https://www.deloitte.com/ie/en/services/consulting/research/milliseconds-make-millions.html) - Deloitte Digital / Fifty-Five (commissioned by Google) (primary)
2. [Store speed and conversion: what the data shows](https://www.shopify.com/enterprise/blog/store-speed-conversion) - Shopify