The verdict in three sentences
On a SaaS marketing site, a 4.1 s mobile LCP costs free-trial sign-ups directly, because visitors decide within seconds whether to stay on the pricing or demo page. An audit at roughly GBP 1,500 to 3,500 in London or USD 2,000 to 5,000 in New York, followed by fixes of GBP 4,500 to 13,000 or USD 6,000 to 18,000, usually gets you under Google's thresholds of LCP below 2.5 s and INP below 200 ms. A realistic goal is 10 to 20% more sign-ups, measured over 6 to 8 weeks before you draw conclusions.
Diagnosis: where the 4.1 seconds come from
The company in this example sells HR software to small and mid-sized businesses with a 14-day free trial. 70% of its traffic is mobile, much of it from LinkedIn or Google Ads. The Search Console Core Web Vitals report flags 62% of mobile URLs as 'needs improvement' or 'poor'. The causes are few: a 6 MB autoplay hero video, a render-blocking custom font and 14 third-party scripts added campaign after campaign.
| Element | Measured weight or time | Main effect | Typical fix |
|---|---|---|---|
| Autoplay hero video | 6 MB | LCP delayed by 1.5 to 2 s | AVIF poster image, video on click |
| 14 third-party scripts (chat, heatmap, pixels, A/B test) | 900 KB, 1.2 s blocking | INP at 380 ms | Prune, defer, load behind consent |
| Custom font not preloaded | 2 files of 120 KB | Invisible text for 0.6 s | Preload, font-display swap |
| Product screenshots in PNG | 2.4 MB per page | LCP and mobile data | AVIF or WebP, explicit dimensions |
| Late-injected cookie banner | 0.3 s | CLS of 0.18 | Reserved space in layout |
| Meeting booking widget | 450 KB | INP on demo page | Load on click |
The 14 scripts deserve a business review: in most audits, 4 to 6 of them are no longer used by anyone. Removing them costs nothing and often solves half the INP problem.
Budget and expected gain
The figures below are 2026 orders of magnitude for a 40 to 80 page marketing site on WordPress, Webflow or Next.js.
| Service | London (GBP) | New York (USD) | Timeline |
|---|---|---|---|
| Core Web Vitals audit and action plan | 1,500 to 3,500 | 2,000 to 5,000 | 1 to 2 weeks |
| Front-end fixes (images, fonts, video) | 2,500 to 6,000 | 3,500 to 8,000 | 2 to 3 weeks |
| Third-party script and consent clean-up | 1,200 to 3,500 | 1,800 to 5,000 | 1 to 2 weeks |
| Partial rebuild of heavy templates | 1,800 to 5,500 | 2,500 to 7,500 | 2 to 4 weeks |
| Field data monitoring (CrUX, RUM) | 120 to 350 per month | 150 to 450 per month | Ongoing |
Total fixes land between GBP 4,500 and 13,000 or USD 6,000 and 18,000 depending on template count and technical debt. Studies published by Google and several vendors report conversion lifts of about 8 to 25% when LCP moves from over 4 s to under 2.5 s. For a free-trial site, a cautious 10 to 20% assumption is a sound basis for the business case.
At Kolonell, audits and fixes are quoted on request after reviewing your field data, and monitoring can sit inside a monthly SEO plan at 100,000, 200,000 or 350,000 FCFA.
Thresholds to target and how to measure
| Metric | Google 'good' threshold | Current value | 8-week target |
|---|---|---|---|
| Mobile LCP (75th percentile) | below 2.5 s | 4.1 s | 2.2 s |
| Mobile INP | below 200 ms | 380 ms | 170 ms |
| CLS | below 0.1 | 0.18 | 0.05 |
| Mobile URLs rated 'good' | 75% or more | 38% | 85% |
| Trial sign-up rate | Internal | 2.0% | 2.2 to 2.4% |
Measure on CrUX field data, which updates on a rolling 28-day window, rather than on a single Lighthouse run. Compare sign-up rate by channel and device, otherwise an ad campaign launched at the same time will distort the reading.
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Mini case study
Rachel, VP Marketing at an HR software company in London, has 30,000 monthly site visits and a 2.0% trial sign-up rate, or 600 trials a month. 12% of trials convert, at an average subscription of GBP 2,000 a year. After a GBP 2,500 audit and GBP 7,500 of fixes, the rate rises to 2.3%, or 690 trials. The extra 90 trials bring about 11 more customers a month, adding GBP 22,000 of annual recurring revenue each month. The GBP 10,000 project pays for itself in the first month of results. A New York team with a USD 2,500 contract value would see about USD 27,500 of added ARR per month on the same numbers.
FAQ
Do Core Web Vitals affect Google rankings?
Yes, but as a secondary signal behind content relevance. Their clearest effect is on conversion, with lifts of 8 to 25% reported across sites.
Should we drop the hero video?
Not necessarily. An 80 to 150 KB poster image with play on click keeps the message while removing 1.5 to 2 s of LCP.
How many third-party scripts should we keep?
There is no official number, but beyond 6 to 8 scripts INP often degrades. Every script needs an owner and a measured purpose.
How fast do results show?
CrUX updates on a rolling 28-day window. Allow 6 to 8 weeks for a reliable read on sign-ups.
Do we need a full rebuild?
Rarely. In about 7 cases out of 10, targeted fixes on 5 to 10 templates are enough to pass the thresholds.
Let's scope your project. Send us your site URL and Search Console access, and we will scope the audit, priority fixes and an 8-week measurement plan. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
