Speed cost calculator
What is a slow website costing you?
Bounce rate does not rise gently with load time — it climbs sharply in the first few seconds, and a fraction of a second is enough to move it. Enter your numbers to model the bounce rate, lost sessions and revenue attached to your current page speed.
Your numbers
Use Largest Contentful Paint from your Lighthouse report if you have it.
2.5s or better is the Core Web Vitals threshold for a good LCP.
Order value, or the value you place on an enquiry.
Modelled opportunity
£301,197
Estimated revenue per year attached to 2.2s of avoidable delay — about £25,100 a month, or £1,141 for every 100ms you remove.
58% → 40%
Modelled bounce rate at the faster load time, a 17.7 point reduction.
+4,416
Extra sessions per month that would stay instead of bouncing.
1.67×
Bounce probability at 4.2s relative to a one-second load.
+295.3
Additional conversions a month, from 450.0 today.
These figures are modelled estimates. They apply published industry averages for bounce probability and conversion sensitivity to the numbers you entered — they are not a measurement of your website or a forecast of your revenue.
The curve
How bounce rate rises with every fraction of a second
Google's mobile research with SOASTA measured bounce probability against load time. The damage is front-loaded: the jump from one to three seconds costs more than the jump from six to ten. Below, your reported bounce rate is projected across the same curve.
- 1s35%
- 2s40%
- 3s46%
- 4s56%
- 5s66%
- 6s72%
- 8s75%
- 10s78%
Projected from your reported bounce rate of 58% at 4.2s, using published relative bounce-probability increases.
Published bounce probability increases
- 1s → 3s
- +32%
- 1s → 5s
- +90%
- 1s → 6s
- +106%
- 1s → 10s
- +123%
Source: Google / SOASTA mobile page speed study. Conversion sensitivity of roughly 0.7% per 100ms comes from published retail performance research.
Where the seconds go
The issues that create the delay you just priced
Oversized images
Uncompressed hero images and missing WebP or AVIF conversion are the most common single cause of a slow Largest Contentful Paint.
Render-blocking scripts
Theme and page-builder bundles that load in full on every page delay first paint and inflate interaction delay.
Server response time
No page or object caching, an old PHP version or an overloaded shared host add fixed delay before anything renders.
Third-party tags
Chat widgets, tracking pixels and embedded feeds each add requests, main-thread work and layout shift.
Common questions
Cost of slow page speed FAQs
Find out your real load time
Run a live Google Lighthouse check to replace the estimate above with your actual LCP, page weight and estimated emissions per pageview.