Lighthouse Score CalculatorSimulate your performance score and find the fastest route to 90
Enter your five lab metrics to get the exact Lighthouse performance score for mobile or desktop, see how many points each metric costs you, and find the target values that would get you to 90.
Reproduces the scoring weights and log-normal curves in the open-source Lighthouse codebase (v13). See Core Web Vitals on web.dev
Updated October 24, 2026
Points lost by each metric (fix the longest bar first)
| Metric | Your value | Metric score | Value for a 90 score | Value for a 50 score |
|---|
How is the Lighthouse performance score calculated?
The Lighthouse performance score is a weighted average of five lab metrics, each scored 0–100 on a log-normal curve: Total Blocking Time 30%, Largest Contentful Paint 25%, Cumulative Layout Shift 25%, First Contentful Paint 10% and Speed Index 10%. Scores of 90–100 are good, 50–89 need improvement and 0–49 are poor.
How to use the Lighthouse score calculator
- Run a test. Use PageSpeed Insights or Chrome DevTools → Lighthouse, and note the five lab metrics: FCP, Speed Index, LCP, TBT and CLS.
- Pick mobile or desktop. The two use different scoring curves. Mobile is what most SEO discussions refer to, and it is harder to score well on.
- Enter or slide the metrics. The score updates instantly, using the same log-normal scoring maths as Lighthouse.
- Fix the longest red bar first. “Points lost” shows how many of the 100 points each metric costs you. The fastest route to 90 tells you the exact target value when one metric can get you there.
How Lighthouse calculates the performance score
Each metric is first converted to a 0–1 score on a log-normal curve with two control points: the value that scores 0.90 (from HTTP Archive’s top-performing sites) and the value that scores 0.50 (the median). Scores above 0.90 get a small boost, then are rounded down to two decimals. The weighted average is rounded to a whole number. This calculator reproduces those steps exactly, following the open-source Lighthouse code.
| Metric (weight) | Mobile: scores 90 | Mobile: scores 50 | Desktop: scores 90 | Desktop: scores 50 |
|---|---|---|---|---|
| First Contentful Paint (10%) | 1.8 s | 3.0 s | 0.93 s | 1.6 s |
| Speed Index (10%) | 3.39 s | 5.8 s | 1.31 s | 2.3 s |
| Largest Contentful Paint (25%) | 2.5 s | 4.0 s | 1.2 s | 2.4 s |
| Total Blocking Time (30%) | 200 ms | 600 ms | 150 ms | 350 ms |
| Cumulative Layout Shift (25%) | 0.10 | 0.25 | 0.10 | 0.25 |
Worked example (the calculator’s default inputs, mobile)
- FCP 2.1 s → 0.81, Speed Index 4.2 s → 0.77, LCP 3.4 s → 0.67, TBT 380 ms → 0.70, CLS 0.08 → 0.94.
- Weighted: 0.81 × 10 + 0.77 × 10 + 0.67 × 25 + 0.70 × 30 + 0.94 × 25 = 77.05, so the performance score is 77.
- Points lost: TBT −9.0 and LCP −8.2 are the big two. Even a perfect TBT would only reach 86, so no single fix gets this page to 90; TBT and LCP together can.
- On the stricter desktop curves, the very same numbers score just 47.
Lighthouse score vs Core Web Vitals
Lighthouse is a lab test
It loads your page once, on a simulated mid-range phone and a throttled connection. That makes it great for debugging, but results vary from run to run, often by 5–10 points.
Core Web Vitals are field data
LCP, INP and CLS measured from real Chrome users over 28 days. This is the page-experience data Google’s ranking systems use, and it is shown at the top of PageSpeed Insights when enough data exists.
| Core Web Vital (field) | Good | Needs improvement | Poor |
|---|---|---|---|
| Largest Contentful Paint (LCP) | ≤ 2.5 s | 2.5–4.0 s | > 4.0 s |
| Interaction to Next Paint (INP) | ≤ 200 ms | 200–500 ms | > 500 ms |
| Cumulative Layout Shift (CLS) | ≤ 0.1 | 0.1–0.25 | > 0.25 |
Does the Lighthouse score affect rankings? Not directly. Google uses Core Web Vitals field data as part of its page experience signals, and relevance matters far more. A higher Lighthouse score usually means faster real-world pages, which helps users and conversions.
How to improve your Lighthouse performance score
Cut main-thread work (TBT)
Defer or delay third-party scripts (chat widgets, trackers, ad tags), remove unused JavaScript and avoid heavy page builders’ extra scripts on pages that do not need them.
Speed up the hero (LCP)
Preload the LCP image, compress it to WebP or AVIF at its displayed size, never lazy-load it, and reduce server response time with caching.
Reserve space (CLS)
Set width and height on images and iframes, reserve slots for ads and cookie banners, and use font-display: swap with matched fallback fonts.
Trim render-blocking CSS (FCP)
Inline critical CSS, load the rest asynchronously, and limit web fonts to the weights you actually use.
Lighten the page (Speed Index)
Fewer, smaller assets above the fold make the page appear complete sooner. Avoid large sliders and video backgrounds on mobile.
Re-test several times
Run three to five tests and use the median. On WordPress, a dedicated caching and optimisation plugin often fixes several of these at once.
Related SEO calculators
Speed is one part of SEO performance. These calculators measure what happens once a fast page ranks.
Lighthouse score questions, answered
It is a weighted average of five metric scores: Total Blocking Time (30%), Largest Contentful Paint (25%), Cumulative Layout Shift (25%), First Contentful Paint (10%) and Speed Index (10%). Each metric is scored on a log-normal curve before weighting.
90 to 100 is good, 50 to 89 needs improvement and 0 to 49 is poor. Most pages find 90+ on mobile hard, because the mobile test simulates a mid-range phone on a slow connection.
Total Blocking Time carries the most weight at 30%, followed by LCP and CLS at 25% each. Reducing JavaScript main-thread work is usually the biggest single lever.
Mobile tests run with CPU and network throttling, and they use separate scoring curves. In practice, mobile scores are usually much lower than desktop scores for the same page.
Lab tests are affected by server response time, network variation, third-party scripts and A/B tests. Run several tests and use the median.
Not directly. Google uses Core Web Vitals field data from real users as part of page experience signals. The Lighthouse score is a lab diagnostic that helps you improve those real-world metrics.
On mobile, LCP scores 90 at 2.5 seconds and 50 at 4.0 seconds. On desktop, the equivalent points are 1.2 and 2.4 seconds.
TBT is the total time between First Contentful Paint and Time to Interactive when the main thread was blocked for more than 50 milliseconds, preventing the page from responding. It is the lab stand-in for Interaction to Next Paint.
It uses the same weights, control points and rounding steps as the open-source Lighthouse code (v13), so the same inputs should produce the same score.
Lighthouse is a single simulated lab test. Core Web Vitals (LCP, INP, CLS) are measured from real Chrome users over 28 days and are what Google's page experience signals use.
Manzoor Ahmad
Web developer & SEO specialist · 13+ years
I have optimised WordPress and Elementor sites for Core Web Vitals for years, including building my own speed plugin for my calculator sites. This calculator is how I decide which metric to attack first before touching any code. Read my full profile.
Published and last reviewed: October 24, 2026
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Sources & references
- Chrome for Developers. Lighthouse performance scoring.
- GoogleChrome / lighthouse (GitHub). Lighthouse source code: metric scoring options and statistics.
- web.dev. Web Vitals.
- Google Search Central. Understanding Core Web Vitals and Google search results.
- Google Search Central. Understanding page experience in Google Search results.
Scores are calculated from the values you enter using Lighthouse’s published scoring model. Lighthouse may change its weights or curves in future versions. Lab scores do not guarantee field Core Web Vitals results or rankings.