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Largest Contentful Paint Calculator

Break LCP into its component phases and find which one to optimise.

About Largest Contentful Paint Calculator

Breaking LCP into its four phases identifies where the time actually goes. A large load delay usually means the resource is discovered late and can be fixed with a preload hint alone. LCP is the heaviest-weighted Core Web Vital, and the 2,500 ms threshold applies at the 75th percentile rather than the average.

Formula

Largest Contentful Paint

LCP = TTFB + resource load delay + resource load time + element render delay

good threshold
2,500 ms at the 75th percentile of real users
load delay
Time between TTFB and the browser starting to fetch the LCP resource

Worked example

With the default values below, Largest Contentful Paint Calculator returns Largest Contentful Paint of 1,850. Change any input above and every figure here is recalculated in your browser.

Inputs used

Time to first byteminimum 0 ms
400 ms
Resource load delayminimum 0 ms
300 ms
Resource load timeminimum 0 ms
900 ms
Element render delayminimum 0 ms
250 ms

Results

Largest Contentful Paint
1,850 ms
Largest Contentful Paint
1.850 s
Rating
Good
Largest Contributing Phase
Resource load time — optimise the image or font itself
Milliseconds to Save to Reach Good
0 ms

Step by step

  1. 1Values used
  2. 2Largest Contentful Paint
  3. 3Largest Contentful Paint= 1,850 ms
  4. 4Largest Contentful Paint= 1.850 s
  5. 5Rating= Good
  6. 6Largest Contributing Phase= Resource load time — optimise the image or font itself
  7. 7Milliseconds to Save to Reach Good= 0 ms

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Largest Contentful Paint calculated?

LCP = TTFB + resource load delay + resource load time + element render delay Breaking LCP into its four phases identifies where the time actually goes. A large load delay usually means the resource is discovered late and can be fixed with a preload hint alone.

Why does Largest Contentful Paint matter?

LCP is the heaviest-weighted Core Web Vital, and the 2,500 ms threshold applies at the 75th percentile rather than the average.

What values do I need to enter?

This calculator takes 4 inputs: Time to first byte, Resource load delay, Resource load time, Element render delay. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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