---
language: en
title: "TBT: Total Blocking Time"
description: "TBT adds up the time by which long tasks exceed the threshold for blocking the browser’s main thread. Learn about lab diagnosis and how it differs from INP."
canonical: "https://tropk.ai/en/resources/glossary/tbt-total-blocking-time"
last_modified: "2026-10-12T16:09:13.724Z"
---

# TBT: Total Blocking Time

Reviewed on 2026-10-07.

## What it means

TBT stands for Total Blocking Time. The metric adds up, over a measurement interval, the portion of long tasks that exceeds 50 milliseconds on the browser’s main thread. While the main thread is busy, the browser cannot interrupt the task to respond immediately to an input. TBT helps investigate potential response delays in a lab setting.

## Why it matters for marketing

For marketing, TBT offers a technical clue when a page loads scripts that compete for execution time. Widgets, components, and third-party code may need investigation, but the metric alone does not identify which resource should be removed. Its purpose is to guide evidence-based diagnosis while preserving important functions such as forms, measurement, and customer support during the technical assessment.

## Example in practice

Imagine a landing page audit records a 180-millisecond task during loading. It contributes 130 milliseconds to TBT, since the calculation considers the time above 50 milliseconds. The team examines the associated script, tests a way to split up the work, and repeats the measurement. It does not attribute all 180 milliseconds to the blocking time calculated by this metric.

## How to apply or check

Use a Lighthouse audit or another lab tool, and record the version, simulated device, network, and interval observed. Review the long tasks and each one’s contribution, comparing runs under equivalent conditions. Then test the interactions that matter to visitors and track [INP](/en/resources/glossary/inp-interaction-to-next-paint) using real-world data. A reduction in loading-related blocking needs to be tied to the problem that prompted the investigation.

## Important distinctions

TBT is not the sum of all JavaScript execution or the total loading time. The interval considered varies by mode and tool, and should be stated in the report. It is an auxiliary metric, outside the [Core Web Vitals](/en/resources/glossary/core-web-vitals). It can indicate risks to INP, but it does not replace that measure: blocking that occurs without an interaction at that moment may not cause a delay perceived by the user.

## Sources and references

- [Total Blocking Time (TBT)  |  Articles  |  web.dev](<https://web.dev/articles/tbt>) — Google / web.dev
- [Web Vitals  |  Articles  |  web.dev](<https://web.dev/articles/vitals>) — Google / web.dev

## Continue a leitura

- [Core Web Vitals](</en/resources/glossary/core-web-vitals>)
- [FCP: First Contentful Paint](</en/resources/glossary/fcp-first-contentful-paint>)
- [INP: Interaction to Next Paint](</en/resources/glossary/inp-interaction-to-next-paint>)

## About the author

[Vinicius Pacheco](</en/team/vinicius-pacheco>)

Responsible for Tropk’s technical content, focusing on crawling, indexing, structured data, and agent access to content.

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