PostHog A/B Testing via Google Tag Manager

A/B test setup, ideation, and creation with PostHog Experiments, managed through Google Tag Manager. We configure feature flags via GTM, set up variant exposure events, define success metrics, and validate consistent variant assignment across sessions.

PostHog Analytics GTM CRO

PostHog A/B testing via GTM: feature flags configured, variant exposure events set up, success metrics defined, and up to 3 experiments running.

Best for

Teams using PostHog who want to run experiments on GTM-managed elements without requiring a developer for every test.

  • 8-14 hours, PostHog GTM setup required
  • Up to 3 experiments per engagement
  • Traffic volume verified for statistical significance at scoping
  • Includes a statistical significance guide for reading results

Overview

How to know if you need PostHog A/B Testing via GTM

  • You are using PostHog and want to run A/B tests on elements managed through GTM without needing a developer for every test.
  • You have test ideas but no structured way to define hypotheses, assign variants, and track exposure events correctly.
  • Previous A/B tests have produced unreliable results because exposure events were not tracked or variant assignment was inconsistent.
  • You want to run experiments on GTM-managed elements (banners, CTAs, layout changes) without deploying code changes for each test.
  • You need a way to read PostHog's experiment results correctly and know when a test has reached a valid conclusion.

What PostHog A/B Testing via GTM covers

  • Test hypotheses defined with a specific success metric for each experiment.
  • PostHog feature flags configured in GTM with variant assignment logic, holdout groups, and correct rollout percentage settings.
  • Variant-specific GTM triggers set up to activate different page modifications or tag behaviour per variant.
  • Experiment exposure events configured so PostHog records which users entered which variant for correct statistical analysis.
  • Statistical significance reference guide delivered so your team can read PostHog's results correctly.

PostHog A/B Testing outcomes

  • Up to 3 experiments running with correct variant assignment, exposure tracking, and success metric events.
  • A testing setup your team can operate independently for future experiments without rebuilding the infrastructure.
  • A statistical significance guide so results are interpreted correctly rather than called early.

PostHog A/B Testing scope and hours

  • 8-14 hours, up to 3 experiments per engagement.
  • Traffic volume is verified at scoping to confirm statistical significance is achievable within a reasonable test duration.
  • Experiments that require application-layer variant rendering are out of scope — this service covers GTM-manageable elements.

What makes our PostHog A/B Testing setup different

  • Hypotheses are defined before any configuration starts. Running tests without a defined success metric produces data, not insight.
  • Exposure events are configured correctly so PostHog's statistical engine has the right data to analyse. Missing exposure events is the most common cause of unreliable experiment results.
  • Traffic volume is confirmed at scoping. We do not set up experiments where statistical significance is not achievable in a practical time frame.
  • You receive a guide for reading results, not just a configured experiment. Knowing when to call a test is as important as running it.

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Our approach

How we deliver PostHog A/B Testing via Google Tag Manager.

A structured process built around your stack, your team, and your data.

01

Hypothesis and metric definition

We work with your team to define test hypotheses and the success metric for each, so experiments answer a clear question rather than just measuring change.

02

Feature flag configuration

PostHog feature flags are configured in GTM with variant assignment logic, holdout groups, and correct rollout percentage settings.

03

Variant triggers

Variant-specific GTM triggers are set up to activate different page modifications or tag behaviour per variant assignment.

04

Exposure event tracking

Experiment exposure events are configured so PostHog records which users entered which variant, enabling correct statistical analysis.

05

Results guide

We deliver a statistical significance reference so your team can read PostHog's results correctly and know when a test has reached a valid conclusion.

Frequently Asked Questions

What is a PostHog feature flag?
A feature flag is a configuration in PostHog that controls which users see which variant of an experiment. It evaluates at page load and returns a variant assignment that GTM can act on to show different content or trigger different tag behaviour.
What is an exposure event?
An exposure event fires when a user is assigned to a variant and actually sees the change being tested. Without exposure events, PostHog cannot distinguish between users who were assigned a variant and users who actually experienced it, which invalidates the statistical analysis.
What elements can be tested via GTM?
Elements managed through GTM: banners, overlays, CTA text changes via DOM manipulation, tag firing behaviour, and form modifications. Elements that require server-side rendering or React state changes are not manageable from GTM.
How long do tests need to run?
Until statistical significance is reached at the traffic volumes your site receives. We estimate test duration at scoping. Running tests for less time than needed is one of the most common causes of invalid conclusions.
Do I need PostHog already set up before this service?
Yes. The PostHog GTM Setup service covers the base installation. A/B Testing requires PostHog to already be collecting events correctly before experiments can be configured.

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