INP or LCP, which one did you actually have to fix?

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Ayanseo

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Core Web Vitals flags both metrics, but the fixes are completely different. LCP is usually about the hero image, web fonts, render blocking CSS or a slow server response. INP is mostly heavy JavaScript, third party scripts, tag managers and long tasks on the main thread.
In audits it's easy to get a long list of fixes and no clear order. Some sites fail one metric only, some fail both, and a lot of sites pass in the lab and fail in the field data.
So I'm curious about real cases. Which metric was the real problem on the sites you work on? What did you change to fix it, and how long did the field data take to catch up in GSC?
And the part I'm most interested in: did rankings or conversions move afterwards, or did only the report go green and nothing else change?
 
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One thing I’ve noticed is that third-party scripts can affect both metrics, but the impact is different. A heavy script might delay the main content and hurt LCP, while also creating long main-thread tasks that affect INP. I’d check script impact before making separate fixes for each metric.
 
Focus on whichever metric is causing the actual user experience issue. LCP affects loading speed, while INP measures responsiveness. I would check real user data first and fix the weaker metric.
 
How long did you wait before checking the results? CrUX uses a rolling 28-day window, so the field data can still include visits from before the fix. A better Lighthouse score right after an update doesn't mean the reported INP or LCP will change at once.
 
I'd like to hear the “report went green but nothing else changed” cases too. A slow checkout button isn't the same problem as a slow hero image, though both show up as CWV issues. With the 28-day field data window, it's actually hard to say whether a later bump in conversions came from the fix.
 
One case I haven't seen covered here is a brand new or small site that doesn't get enough traffic to show any field data in Search Console yet. Without real-user numbers you're left with lab tests, and those aren't great at showing responsiveness problems. So how do you decide whether INP or LCP is the real issue in that situation? Is it better to set up your own real-user tracking first, or just start with LCP because it's easier to see?
 
house wife said:
One case I haven't seen covered here is a brand new or small site that doesn't get enough traffic to show any field data in Search Console yet. Without real-user numbers you're left with lab tests, and those aren't great at showing responsiveness problems. So how do you decide whether INP or LCP is the real issue in that situation? Is it better to set up your own real-user tracking first, or just start with LCP because it's easier to see?
Click to expand...
I wouldn’t assume from LCP alone. Configure RUM to monitor mobile users, but it should be as lightweight as possible; lab testing is good for finding suspects, not diagnosing INP.
 
Ayanseo said:
Core Web Vitals flags both metrics, but the fixes are completely different. LCP is usually about the hero image, web fonts, render blocking CSS or a slow server response. INP is mostly heavy JavaScript, third party scripts, tag managers and long tasks on the main thread.
In audits it's easy to get a long list of fixes and no clear order. Some sites fail one metric only, some fail both, and a lot of sites pass in the lab and fail in the field data.
So I'm curious about real cases. Which metric was the real problem on the sites you work on? What did you change to fix it, and how long did the field data take to catch up in GSC?
And the part I'm most interested in: did rankings or conversions move afterwards, or did only the report go green and nothing else change?
Click to expand...
In my experience, while LCP is usually straightforward to solve by preloading hero assets and optimizing fonts, INP is the real bottleneck due to heavy third-party scripts and tag managers. While fixing CWV rarely triggers a sudden ranking boost on its own, acting more as a tie-breaker in competitive SERP - reducing INP lag directly improves user experience, resulting in noticeably lower bounce rates and better conversion rates.
 
I prioritise fixes based on real user impact rather than trying to clear every warning in an audit. Also field data takes time to reflect changes.
 
LCP for us almost every time, mostly on wordpress sites where the hero image was lazy loaded by the theme. turning off lazy load just for that one image fixed it on a few sites. INP only ever came up on a client site with like 4 chat and tracking widgets running
 
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