How much does a slow website cost? Calculate the revenue you’re leaving behind
Nobody enjoys waiting for a page to load. On mobile, with a patchy signal, every second of waiting is an invitation to go back to Google and click on a competitor. The effect shows up in three places: more abandonment before the page opens, less conversion from those who stay and ads paying for clicks that never saw the offer.
How much slowness may be costing you
Industry studies over the years have linked each extra second of loading to conversion drops that vary widely by sector and type of site. That’s why the calculator below doesn’t give a fixed number: it uses an adjustable assumption of drop per second. Start with a conservative value and compare scenarios.
Estimated revenue lost to slowness
Use data from a typical month for your site or store.
Illustrative estimate: the conversion drop is compounded for each extra second. The real impact depends on audience, device and page — which is why Manáry measures before promising any gain.
What to actually measure
Google uses three metrics, called Core Web Vitals, to describe the loading and interaction experience. The thresholds considered good are:
| Metric | What it measures | Good |
|---|---|---|
| LCP — Largest Contentful Paint | Time until the largest visible element loads | up to 2.5 s |
| INP — Interaction to Next Paint | Response time to clicks and taps | up to 200 ms |
| CLS — Cumulative Layout Shift | How much the layout “jumps” while loading | up to 0.1 |
Field data, from real Chrome visitors, appears in Search Console’s Core Web Vitals report and in PageSpeed Insights. That’s what matters — a pretty lab test on fiber doesn’t represent someone buying on their phone on the subway.
The most common causes
Images far too large
3,000-pixel photos displayed at 400 pixels, uncompressed and in an old format. Formats like WebP and AVIF and correct sizing are usually the quickest win.
Third-party scripts piling up
Chat, pixels, heatmaps, review widgets: each adds weight and competes for the browser’s processing — and mainly hurts INP.
Heavy theme or page builder
Themes that load every resource on every page, even when not used.
Hosting and caching
A slow server responds late before any front-end optimization can take effect. Page caching and a CDN cut that time.
Elements with no set dimensions
Banners and images without declared width and height push content around while loading — the main cause of high CLS.
How to measure your site’s speed in 10 minutes
Open PageSpeed Insights
Paste the URL of the most important page — the home page, a product page or the campaigns’ landing page.
Look at field data first
The real-user data section shows LCP, INP and CLS for people visiting the site in Chrome. It’s more reliable than the lab score.
Compare mobile and desktop
On most sites, mobile is much slower — and it’s where most media traffic comes from.
Check Search Console
The Core Web Vitals report groups pages by status and shows which page templates have problems.
Note the three biggest opportunities
Images, third-party scripts and server response time usually top the list.
Speed also affects the cost of paid media
When the page is slow, some of the people who clicked the ad give up before seeing the offer. The click was paid for, but the visit never happened. On top of that, landing page experience is one of the components of Quality Score in Google Ads, which influences ad position and cost. A fast site makes the same budget deliver more real visits and more conversions.
What you can improve without rebuilding the site
| Improvement | Effort | Typical impact |
|---|---|---|
| Compress and convert images to WebP or AVIF | Low | High on LCP |
| Set width and height for images and banners | Low | High on CLS |
| Remove unused plugins and scripts | Medium | High on INP |
| Enable page caching and a CDN | Medium | High on response time |
| Defer chat, map and video scripts | Medium | Medium to high |
| Replace a heavy theme or page builder | High | High, when the problem is structural |
Most of the gains come from the first rows of the table. Rebuilding the site is only justified when the structure prevents any meaningful improvement — and then the project goes through the four approvals described in Web Dev & Infrastructure.
Frequently asked questions
What is the ideal website speed?
By Google’s criteria, the page’s largest visible element should load within 2.5 seconds (LCP), responses to interactions should take up to 200 milliseconds (INP) and visual instability should stay at 0.1 or below (CLS).
Does a slow site lose rankings on Google?
Page experience is considered by Google’s ranking systems, but content relevance is still more important. Slowness mostly weighs between pages with similar content.
Does more expensive hosting fix slowness?
It can when the bottleneck is server response time. If the problem is heavy images or too many scripts, switching hosting changes little.
How often should speed be measured?
After every significant change to the site and, at a minimum, monthly through Search Console, which shows the trend with real user data.
Want to know how much your site is leaving on the table?
We measure speed with real data, map the conversion path and deliver the list of what to fix in order of impact.
Your result is one step away
Enter your details to unlock this and every other result from Manáry’s tools. It’s free and takes less than a minute.
Want to apply this to your business?
Manáry looks at your real numbers — media, website and CRM — and hands back the priorities in order of impact.
Get the next pieces by email
Calculators, checklists and practical guides. No spam, one-click unsubscribe.