Lighthouse Score Estimator
Predict your Lighthouse Performance score from Core Web Vitals
Plug in FCP, LCP, TBT, CLS, and Speed Index — see the Lighthouse Performance score those numbers would produce, with Lighthouse 10 weights.
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What is a Lighthouse Score Estimator?
Lighthouse turns five Core Web Vitals into a single 0–100 Performance score using a weighted log-normal distribution. The weights changed in Lighthouse 10 — Total Blocking Time now matters more than Largest Contentful Paint, and First Contentful Paint dropped from 15% to 10%. If your mental model is from a 2022 audit, your priorities are wrong.
This estimator takes the same five metrics Lighthouse measures and runs them through the official LH10 scoring curves. You get the predicted Performance score plus a per-metric breakdown showing which numbers are dragging the total down.
Use it before commissioning a frontend optimisation sprint to see which metric to prioritise, or to predict whether a planned change (e.g. removing a 200ms third-party script) will move the needle. It is not a substitute for running real Lighthouse — but it tells you what running it will return.
Why use this Lighthouse Score Estimator
Built for Indians, by Indians. Every number, every formula, every slab — tuned to FY 2026-27 reality.
Lighthouse 10 weights
Uses the latest scoring weights — TBT 30%, LCP 25%, CLS 25%, FCP 10%, SI 10%.
Per-metric breakdown
See which Core Web Vital is dragging your score down before you start optimising.
Run what-if scenarios
Drop your TBT by 100ms and see the score lift instantly. Decide whether the work is worth it.
Browser-only
No URL fetched, no third-party API. Numbers stay local.
Using the Lighthouse Score Estimator in 4 steps
No onboarding, no signup. Answer three fields and the numbers update live.
Run real Lighthouse first
Use Chrome DevTools or PageSpeed Insights to get your current FCP, LCP, TBT, CLS, and Speed Index.
Enter the metrics
Paste each value. Times in milliseconds, CLS as decimal (0.05, 0.10).
Read the score
See the predicted 0–100 score and the per-metric contribution breakdown.
Run scenarios
Adjust one metric at a time to test "if I fix this, what happens?".
Tips to get the most out of it
TBT is the biggest lever — at 30% weight, every 50ms of blocking script removed has roughly the same impact as a 100ms LCP improvement.
CLS is binary in practice — anything above 0.25 puts you in the red zone. Prioritise reserving image dimensions and avoiding late-injected content.
Speed Index correlates highly with FCP and LCP — if you fix those, SI usually fixes itself. Don't chase it as a separate metric.
A predicted 90+ score is mobile-realistic only if you also test on slow 4G with mid-tier CPU throttling. Desktop Lighthouse will overstate by 10-20 points.
Real-world scenarios
How Indians actually use this estimator — concrete inputs, concrete outcomes.
Pre-sprint priority check
Frontend team has FCP 1.8s, LCP 3.2s, TBT 320ms, CLS 0.08, SI 2.4s. Estimator returns 62. Reducing TBT to 150ms (lazy-loading two third-party scripts) lifts the predicted score to 78.
Sales-team-friendly forecast
Agency sells a "performance package" to a client. Plugs in current metrics, then projected post-optimisation metrics. Generates a "62 → 92" forecast for the proposal deck.
CI gate threshold
DevOps decides to fail PRs if predicted Lighthouse drops below 85. Uses this tool to figure out which metric thresholds correspond to that score, then sets per-metric budgets in Lighthouse CI.
Frequently Asked Questions
Still have a question? Our team replies within a business day.
It uses the same Lighthouse 10 weights and the published scoring curves for each metric. Predictions land within 1-2 points of real Lighthouse runs in most cases.
Lighthouse runs throttling on top of your input metrics, plus checks runtime issues like main-thread bottlenecks and third-party blocking. The estimator only scores what you tell it.
No — only the Performance category. The other three are checklist-based and can't be predicted from numerical inputs.
Yes. Mobile uses stricter thresholds. Run real Lighthouse with mobile emulation to know which curve you are on, then plug those mobile-throttled numbers into the estimator.
Run Lighthouse in Chrome DevTools (Mobile preset, slow 4G), use PageSpeed Insights, or pull from CrUX / Search Console for real-user data.
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