Website Speed Impact Calculator
This website speed impact calculator helps site owners estimate how slower load times could affect visits, conversions, and sales. Enter your load time, bounce rate, monthly visitors, and average order value to see modelled monthly losses based on the tool's assumptions.
What this tool measures
Slow pages lose visitors before they see anything. This calculator estimates how many monthly visits, conversions and sales could be affected by a load time above three seconds, using your traffic and order value and a simple set of assumptions.
It is a planning aid, not a measurement of your site. Measure real load time with Lighthouse, PageSpeed Insights or your own field data first, then use this to frame what the delay might cost.
How to read each field
- Current Load Time (seconds)
- How long a typical visitor waits for the page to become usable. Use a field figure such as the median from real-user data if you have one, not a single lab run.
- Current Bounce Rate
- The share of visits that leave after one page, taken from your analytics.
- Monthly Visitors
- Sessions per month to the pages you are assessing.
- Average Order Value
- Revenue per conversion. For lead generation use the value of a won customer, or a typical first sale.
- Adjusted bounce, lost visitors, lost conversions, revenue lost
- The tool assumes bounce rate rises by about seven percentage points for each second beyond three. It then converts the extra bounces into visitors lost, applies an assumed 2.5% conversion rate to get conversions lost, and multiplies by order value.
Worked example
An online shop loads in 5 seconds, has a 50% bounce rate, 10,000 monthly visitors and an average order of 100. The page is 2 seconds over the three-second line, so bounce rate is assumed to rise by 14 points, from 50% to 64%. That is 1,400 visitors lost per month. At the assumed 2.5% conversion rate, about 35 sales are affected, which is 3,500 in monthly revenue.
If the same shop gets the page down to 3 seconds, the extra bounce is zero and the estimate falls to zero. The figure is not a forecast of what you will gain; it shows the scale of what is at stake so you can decide how much engineering time a speed project deserves.
Limits to keep in mind
- The seven-points-per-second rule and the 2.5% conversion rate are fixed planning assumptions, not measurements of your site. Real sensitivity varies by device, audience and page type.
- A faster page will not automatically recover the full estimate. Offers, trust and the checkout also affect conversion.
- The tool does not test your site. It takes a load time you enter.
Frequently asked questions
Why does the calculator use three seconds?
It is a common planning threshold for mobile pages, below which the model assumes no extra bounce. It is a simplification, not a rule from Google.
How do I find my real load time?
Run PageSpeed Insights or Lighthouse on your key pages, and check the real-user section if your site has enough traffic. Compare mobile and desktop separately.
Can I use my own conversion rate?
The calculator uses a fixed 2.5% so results are comparable. If your rate differs, scale the lost-conversions and revenue figures by your rate divided by 2.5.
Terms explained
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