At a glance
Largest Contentful Paint p75 over time, daily or monthly time-series of mobile LCP measured from CrUX. The drift-detection view that surfaces gradual performance degradation (or improvement) the static crux_lcp_p75 snapshot can’t show. Critical for monitoring because LCP drift often happens slowly (added third-party tags, image-quality drift on uploaded content, CDN config changes) and goes unnoticed until it crosses a threshold weeks later.
Calculation
Calculated automatically from your Website Performance (PageSpeed + CrUX) data. See the At a glance summary above for what the metric tracks and the worked example below for a typical reading.Worked example
A UK-based BigCommerce fashion store, mobile LCP trend over 6 months ending Wednesday 15 May 26.
What the trend is telling us:
- The site has more than doubled its LCP over 6 months without anyone noticing. Each individual month-over-month change looked modest (80-660ms); cumulatively the LCP has gone from healthy good-band (2,380ms) to failing poor-band (4,820ms). No single deploy was clearly catastrophic; the drift is the story.
- Three distinct contributing events can be identified from the inflection points: (a) Feb 26 hero carousel deploy (+460ms): a marketing-driven design refresh that added heavier hero imagery without performance review; (b) Mar 26 marketing-stack expansion (+660ms): three new third-party tags added in a single sprint to support a new email and chat strategy; (c) Apr 26 BFCM-prep campaign images (+580ms): heavy seasonal imagery uploaded without optimisation discipline.
- Each contributing event individually felt acceptable to the team that made it. The hero carousel was visually stunning; the marketing stack expanded customer engagement; the BFCM imagery was on-brand. None of the teams making changes saw the cumulative LCP impact because nobody was watching the trend.
- The recovery path requires reversing each contribution thoughtfully. Image format conversion + responsive variants for hero + product images recovers ~1,500-2,000ms. Third-party tag deferral + GTM audit recovers another 400-600ms. Aggressive caching + CDN tuning recovers another 200-400ms. Cumulative recovery target: 4,820ms → 2,200-2,400ms over a focused 6-week optimisation cycle.
- Future protection: trend monitoring as a guardrail. Set an alert at +200ms vs 30-day baseline so the next 200ms drift is caught immediately and traced to its cause. Prevents the next 6-month cumulative regression. The Vortex Mind Pre-Launch Readiness report can fire alerts on this signal.
- The 28-day rolling window’s effect on the trend curve is visible in the smoothness. A real-world step regression (e.g. the Mar 26 marketing-stack add) appears as a gradual rise over 28 days rather than a vertical cliff. For attribution work, look 7-14 days before the inflection to find the actual regression event date.
- Identify the dominant trend direction. Up over months = drift; sharp step = single regression event.
- Cross-reference inflection points with deploy log + content management activity. Most regressions trace to a specific date.
- Decompose into component contributions. Was it third-party? First-party? Content uploads? Each cause has a different fix.
- Plan recovery to undo each contribution. Multi-week cycle typical for accumulated drift.
Sibling cards merchants should reference together
Reconciling against the vendor’s own dashboard
Where to look:- GSC → Core Web Vitals report, surfaces 90-day trend.
- CrUX Dashboard via Looker Studio, Google’s official CrUX explorer with deeper trend analysis.
- CrUX BigQuery dataset, monthly snapshots back to 2018 for long-term historical analysis.
Cross-connector reconciliation: primarily internal (with
crux_lcp_p75, psi_score_trend).
Quick rule for support tickets: if a merchant says “I deployed a fix yesterday but the trend hasn’t moved”, the 28-day rolling window means yesterday’s fix is one day in a 28-day average. Wait 7-14 days for partial movement; 28 days for full reflection.
Known limitations / merchant FAQs
My LCP has crept up 800ms over 6 months. Where do I start the recovery? Cross-reference inflection points with deploy + content-management activity. Most cumulative drift traces to specific events (a deploy, a content upload, a third-party tag addition); identifying the events lets you reverse them. Tools to use: deploy log, GTM audit log, CMS image-upload log, theme version history. My trend looks flat but my LCP is in the poor band. What do I do? The site has a stable but bad LCP. No drift means no recent regression; the issue is structural rather than progressive. Address structural issues: image format conversion, render-blocking CSS, slow server response. The optimisation playbook is the same as for a recently-regressed site, just no need for inflection-point investigation. My deploy fixed LCP but the trend hasn’t moved. Why? The 28-day rolling window. Each daily data point includes 27 days of pre-deploy data plus 1 day of post-deploy. Wait 7 days for partial movement (then ~25 percent of the window is post-deploy); 14 days for substantial movement; 28 days for full reflection. Why is my trend so smooth when I know my deploys have spikes? The 28-day rolling window smooths spikes. Sharp single-day regressions appear as gradual rises in the trend view. For attribution work, the inflection point in the trend lags the actual regression event by ~7-14 days; look earlier than the visible inflection. Should I use trend or snapshot? Both. Snapshot answers “where am I now”; trend answers “where am I going”. Use snapshot for ranking-impact decisions today; use trend for drift detection and recovery planning. Can Vortex IQ alert me when LCP starts drifting? Yes; alert trigger7-day rolling delta > +500ms catches step regressions; current value > 2,500ms catches threshold crossings. Configure in Vortex IQ → Alerts.
Why does my trend show null for some recent days?
Insufficient CrUX data for those windows. Sites with low or fluctuating traffic occasionally drop below the 1,000-session threshold; the metric returns null for affected days. Use lab data (psi_lab_lcp) as the fallback for those gaps.
Can I export this trend to share with stakeholders?
The Vortex IQ dashboard supports CSV export; the underlying CrUX BigQuery dataset is also publicly queryable for long-form reporting. The Vortex Mind Pre-Launch Readiness report includes trend snapshots in its outputs.