Site Speed Impact Calculator
The calculator uses real Chrome user data to show how many page loads on your site miss good Core Web Vitals and puts up to two competitors next to it. Add your monthly visits for an estimate of the affected visits, and your conversion rate and conversion value for an estimate of what faster, more stable loading could be worth. Free, no sign-up.
Page loads that are not good, from real users instead of a lab score
The calculator uses the Chrome UX Report: what real Chrome users experienced on your site over the last 28 days. For Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift it shows the share of page loads that need improvement or are poor and how far each metric is from passing, next to your competitors. A lab score from a single simulated page load cannot show this, because it does not tell you how many visitors were affected.
From page loads that are not good to visits and revenue
Enter your monthly visits for an estimate of how many were affected. Add your conversion rate and the value of a conversion to estimate what faster, more stable loading could be worth. The calculator applies a conversion lift only to the affected visits, uses the metric with the largest share of page loads that are not good as the base and rounds down. The default is a lift of 5 to 10 percent on those visits; case studies measure their effects across all visitors of the tested pages.
What causes the slow LCP
For pages whose largest element is an image, the Chrome UX Report splits LCP into server response, load delay, load duration and render delay. The calculator shows the longest subpart and links to the guide for fixing it.
Frequently asked questions
Where does the data come from?
From Google's Chrome UX Report, the same field data Google uses to assess Core Web Vitals. It covers the last 28 days and is updated daily.
What does the estimate assume?
It assumes that all affected page loads are good after the optimization and applies the lift only to those visits. It uses the single metric with the most page loads that are not good instead of adding metrics up, and rounds money, visits and conversions down.
Are my business numbers stored?
No. Visits, conversion rate and value per conversion are calculated in your browser and never sent to PerfDelta.
Why does my site show no data?
The Chrome UX Report only includes sites with enough Chrome traffic. Smaller sites have no field data; a lab test is the next step for them.
How is this different from PageSpeed Insights?
The score in PageSpeed Insights is a lab simulation. This calculator uses only field data and adds the share of affected visits, the competitor comparison and the estimate.
More free tools
A free account saves your tests and shows how your values change from one test to the next. Daily monitoring with field data and alerts starts with the Solo plan.