Slow Website Cost Calculator
Put in your monthly visitors, conversion rate and value per conversion, plus how long the site takes to load now — and see roughly what the wait costs in lost enquiries or sales, per month and per year. Every number is yours except one: the model assumes 5 % of would-be conversions lost per second, set lower than the published load-time studies suggest.
A free calculator that turns website speed into money: enter monthly visitors, conversion rate, value per conversion and your current load time, and see an estimate of what each extra second costs in lost enquiries or sales per month and per year. It assumes a 5 % conversion loss per second above two seconds, set lower than the published load-time studies suggest. Runs in your browser.
A visitor who leaves before the page loads never becomes an enquiry — and there is no record of the enquiry you lost.
Your traffic, your conversion rate, your load time: the number, in money.
Don’t know your load time? Get it free from PageSpeed Insights ↗ (mobile, the LCP figure). The speed check on this site times your server’s first response and weighs what the page loads, but it does not measure LCP — use it to see why the page is slow.
$900
a month · $10,800 a year · about 8 lost enquiries or sales every month
- Seconds over target
- 2.5 s
- Would-be conversions lost
- about 13%
- Each extra second costs
- ≈ $360 / month
- Recovered by reaching the target
- $900 / month
Model: revenue at the target speed = visitors × conversion rate × value. Every second slower than the target (floor 2 s) is assumed to lose 5% of would-be conversions, capped at 80 %. That 5% is an assumption, set lower than the published studies suggest: Akamai (2017) saw conversion rates drop 7 % with a 100 ms delay, and Deloitte (2020) saw retail conversions rise 8.4 % when mobile pages got 0.1 s faster. An estimate to compare scenarios with, not a forecast.
Runs in your browser — nothing is uploaded, nothing is stored. Close the tab and it is gone.
What the research says
How load time changes what mobile visitors do
Google measured real mobile visits, and Deloitte measured what a tenth of a second was worth across 37 brand sites. The green band is the load time Google calls good.
At 3.0 s a mobile visitor is +32% more likely to leave than at 1 s, as Google published it. Measure your page →
The rise after mobile pages got 0.1 seconds faster.
- Retail conversion rate8.4%
- Retail spend per order9.2%
- Travel conversion rate10.1%
These figures are other people’s research, quoted as published. Your own site’s numbers come from the free checks and the audit.
After a speed job
Your page, loading faster on a phone
Left: the page as it loads today, with the wait you entered above costing enquiries every month. Right: the same page after a speed job. The images are sized for where they sit, the scripts that block the page are deferred, and caching is switched on, so the estimate above gets smaller.
- Images resized and converted for where they sit
- Blocking scripts deferred or removed
- Caching and compression on, then the page measured again
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Schedule a Meeting
Bring the estimate and your PageSpeed figure. I lead every project, and on the call we go through what is slowing the page and decide what to fix first.
How it works
How to use the Slow Website Cost Calculator
- 01Enter visitors per month, conversion rate and the value of one conversion.
- 02Enter the current load time (the mobile LCP figure from PageSpeed Insights) and a target.
- 03Read the monthly and yearly estimate — then decide whether a speed job pays for itself.
Good to know
Where the 5 % per second comes from
It is an assumption, kept cautious. The published studies measured different things: Google and SOASTA (2017) found a mobile visitor 32 % more likely to bounce at 3 seconds than at 1; Akamai (2017) saw conversion rates drop 7 % with a 100-millisecond delay, and Deloitte's Milliseconds Make Millions (2020) saw retail conversions rise 8.4 % when mobile pages got 0.1 seconds faster. None of them gives one per-second figure for every site, so the calculator uses 5 % for each second above a 2-second floor and caps the loss at 80 % so the estimate stays sensible for very slow sites.
In more depth
About the slow website cost calculator
What the calculator turns 'slow' into
'Your site is slow' is hard to act on. Put in your own numbers — visitors, conversion rate, what one sale or enquiry is worth, and the load time — and it becomes a figure per month that you can weigh against the cost of fixing it.
A speed fix is usually a fixed-scope job. If the monthly figure is bigger than what the fix costs, the fix pays for itself. If it is smaller, you know the money is better spent somewhere else.
FAQ
Slow Website Cost Calculator — questions
Where do I get my load time?
- Run the page through Google PageSpeed Insights and take the mobile Largest Contentful Paint, or use the speed check on this site for the page-weight facts behind it.
Is 5 % per second accurate for my site?
- It is an assumption, not a measured figure, and it is set lower than the published studies suggest: Akamai (2017) saw conversion rates drop 7 % with a 100-millisecond delay, and Deloitte's Milliseconds Make Millions (2020) saw retail conversions rise 8.4 % when mobile pages got 0.1 seconds faster. Your real figure depends on the audience and device mix; use the tool to compare scenarios, not to forecast an exact amount.
What counts as a conversion for a service business?
- An enquiry — a form, a call, a WhatsApp message. Value per conversion is what an average new enquiry is worth to you (lead value × close rate), not just an order total.
What is a good load time?
- Google's 'good' threshold for Largest Contentful Paint is 2.5 seconds on mobile. If your page is above it, large images are the first thing to check, and the image tools on this site resize them.
More tools
The other tools
WordPress Site Check
The flagship check for WordPress sites: setup, every plugin and the theme against wordpress.org (stale, closed, outdated), and a light security read — one score, one fix list.
Open →SEO Checker (Light)
The light version: paste a page URL for 16 automated on-page checks with a fix for each.
Open →Speed Check (Light)
The light version: how fast your server answers and how heavy the page is, measured from our server, with a fix for each finding.
Open →Google Snippet Preview
Type a title and description and see the Google result on desktop and mobile — with the real pixel cut-off.
Open →Social Link Preview
See how a link looks on Facebook, LinkedIn, X and WhatsApp — fetch the tags from a page or write them, then copy them.
Open →Robots & Sitemap Checker
Is Google allowed in? Reads your robots.txt and XML sitemap and flags a blocked site, blocked assets, a missing or empty sitemap.
Open →Schema Markup Generator
Fill a form, get valid JSON-LD for a local business, organization, FAQ, product, article or breadcrumbs.
Open →Keyword & Content Analyzer
Paste a draft: word count, reading time, readability grade, keyword and phrase density, headings — with a focus-keyword check.
Open →UTM Link Builder
Tag a link with source, medium and campaign so Google Analytics shows which post, ad or email brought the visit.
Open →Colour Contrast Checker
Text on background → the WCAG contrast ratio, AA/AAA verdicts, a live sample and the nearest passing shade.
Open →Favicon & App Icon Generator
One logo → favicon.ico, every PNG size, Apple touch icon, Android icons, a maskable icon, the manifest and the head code — as a zip.
Open →Image Optimizer
Compress and resize up to five images at once; keeps each format and the aspect ratio, shows the before/after size.
Open →Image to WebP Converter
Convert JPG and PNG to WebP for smaller files that still look sharp.
Open →Image to WebP Converter with Resize
Convert to WebP and set the width or height in one step.
Open →Image Resize & Crop
Crop to exact pixel sizes, several from one image — for hero images, thumbnails and share images.
Open →Password Generator
Strong random passwords — length, letters, numbers and symbols, your choice.
Open →Passphrase Generator
Real-word passphrases from the EFF list, 3–8 words, with the word list to learn them by.
Open →Password Strength Checker
See how a password holds up — checked on your device, never sent anywhere.
Open →
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