# Shopify PageSpeed: Why 99/100 Is Not the Goal

> Shopify PageSpeed: Lighthouse, TBT, INP and real Core Web Vitals. Optimize performance without chasing 100/100 or conversion guarantees.

- Author: [Francesco Guiducci](https://ifgdigital.com/en/francesco-guiducci/)
- Published: 2026-04-24 · Updated: 2026-09-03
- Topic: [Performance and theme code](https://ifgdigital.com/en/ifgwebdesign/ecommerce/blog/topic/performance/)
- Language: English · Italian version: https://ifgdigital.com/ifgwebdesign/ecommerce/blog/performance-shopify-oltre-99-pagespeed-tbt/
- Reading time: 1 min
- URL: https://ifgdigital.com/en/ifgwebdesign/ecommerce/blog/shopify-pagespeed-why-100-is-not-the-goal/

**Direct answer:** a PageSpeed score of 99 or 100 does not eliminate cart abandonment and does not guarantee conversions. Lighthouse is a lab test. I use it as diagnostic evidence and compare it with real Core Web Vitals and the behavior of the actual template and device.

## PageSpeed is not real traffic

The test simulates defined conditions and produces a synthetic score. It can reveal opportunities but cannot replace field data from real users.

## TBT and INP are different

Total Blocking Time is a lab metric that highlights main-thread blocking JavaScript. INP is a Core Web Vital measured across interactions. Lower TBT can help, but there is no fixed numerical relationship between TBT, INP and conversion.

## The thresholds I use

Google's “good” thresholds are LCP within 2.5 s, INP within 200 ms and CLS within 0.1 at the 75th percentile. I do not invent a private threshold and turn it into a sales claim.

## What I check on Shopify

- LCP image and resources;
- theme and app JavaScript;
- CSS, fonts and layout shifts;
- Liquid rendering;
- assets loaded where they are not needed;
- mobile regressions after changes.

## Do not break the store for a score

Blindly deferring scripts can break variants, analytics, popups, apps or cart behavior. Every optimization needs a functional regression test, not only a better score screenshot.

## Performance and business

A more responsive page removes a real friction, but revenue also depends on product, price, traffic, trust and checkout. I do not assign generic ROI tables to milliseconds.

*Updated September 3, 2026.*