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    GA4 vs PostHog: Which Analytics Platform Should You Choose?

    A practical comparison of Google Analytics 4 and PostHog from a product engineer's perspective, helping you choose the right analytics tool for your needs.

    GA4 vs PostHog: Which Analytics Platform Should You Choose?

    After working with both Google Analytics 4 and PostHog across different projects, I've learned that choosing an analytics platform isn't just about features—it's about understanding what questions you're trying to answer and who will be asking them.

    GA4 and PostHog represent two fundamentally different philosophies. GA4 is Google's enterprise-grade platform built for marketers tracking acquisition and campaigns. PostHog is an open-source, developer-first toolkit built for product teams who need to understand how users interact with their product, not just where they came from.

    Here's what I've learned using both, and how to decide which one fits your needs.

    The Core Difference

    Before diving into features, understand this: GA4 is built for marketing teams; PostHog is built for product teams.

    GA4 excels at answering questions like:

    PostHog excels at answering questions like:

    Both can answer each other's questions, but they're optimized for different use cases. This distinction matters more than any feature comparison.

    What Each Platform Actually Offers

    GA4: The Marketing Powerhouse

    What you get:

    What you don't get:

    PostHog: The Product Engineer's Toolkit

    What you get:

    What you don't get:

    The Features That Actually Matter

    Here's what I care about when choosing analytics:

    Event Tracking & Custom Properties

    GA4 limits you to 25 custom user properties and 50 custom event parameters. For most marketing use cases, this is plenty.

    PostHog has no limits. Track whatever you want, however you want. As a developer, this matters when you're iterating fast and need flexibility.

    Funnels & Retention

    Both handle funnels, but PostHog's funnel analysis is significantly more powerful. You can break down funnels by any property, compare cohorts, and dive deep into where users drop off. GA4's funnels work, but they feel basic once you've used PostHog's.

    Session Replay

    This is a game-changer for debugging UX issues. PostHog includes privacy-aware session replay that automatically masks sensitive inputs. Watching a user struggle with your checkout flow tells you more than any funnel chart ever could.

    GA4 doesn't have this. You'd need to add Hotjar, FullStory, or LogRocket separately.

    Feature Flags & A/B Testing

    PostHog's built-in feature flags let you roll out features gradually, do multivariate testing, and control who sees what—all in the same tool where you're measuring impact.

    GA4 used to integrate with Google Optimize, but Google shut it down in 2023. Now you need a separate tool like Optimizely or VWO.

    Data Ownership

    With GA4, your data lives on Google's servers. You can export to BigQuery, but that's another tool to manage.

    With PostHog, you can self-host and own every byte, or use their cloud with easy exports to S3, Snowflake, or your data warehouse.

    What This Actually Costs

    GA4: Free Until It's Not

    GA4's free tier is generous: 10 million events per month for web properties. For most sites, that's effectively unlimited.

    If you outgrow the free tier, GA4 360 starts around $50,000/year and scales based on volume. That's a massive jump, but you're getting enterprise support, SLAs, and advanced features like roll-up reporting.

    Bottom line: Free for 99% of projects. If you need more, you're paying enterprise prices.

    PostHog: Pay for What You Use

    PostHog gives you 1 million events free every month, plus access to all features (session replay, feature flags, experiments).

    After that, it's usage-based:

    For a project with 10 million events/month, you're looking at around $2,800/month for analytics alone. But you're also getting session replay, feature flags, and A/B testing—features that would cost thousands more with separate tools.

    Bottom line: Generous free tier for side projects and MVPs. As you scale, costs are predictable and linear.

    When to Choose GA4

    Use GA4 if you're:

    Running a marketing-driven business. Your primary goal is tracking where traffic comes from, which campaigns convert, and how to optimize ad spend. GA4's integration with Google Ads is unmatched.

    Already in the Google ecosystem. If you're using Google Ads, Tag Manager, Search Console, and BigQuery, GA4 fits seamlessly into your workflow.

    Operating at massive scale with minimal budget. You need to track billions of events and can't justify spending thousands on analytics. GA4's free tier scales incredibly well.

    Building a content site or e-commerce store. Standard analytics questions (pageviews, bounce rate, conversion tracking) are what you care about, and GA4 handles these effortlessly.

    Working in a heavily regulated environment. You want a vendor that handles compliance, requires zero infrastructure, and has brand recognition with stakeholders.

    When GA4 Falls Short

    Don't choose GA4 if you need to:

    When to Choose PostHog

    Use PostHog if you're:

    Building a product-led SaaS business. You need to understand feature adoption, retention cohorts, and user behavior at a granular level. PostHog is built for this.

    Tired of stitching together multiple tools. Instead of paying for Amplitude + LaunchDarkly + FullStory + Statsig, you get everything in one platform.

    Working on a team that writes code. Your PMs and engineers want SQL access, programmatic API control, and the ability to self-serve insights without waiting for analytics specialists.

    Required to self-host for compliance. HIPAA, GDPR data residency laws, or internal policies mean you need complete control over where data lives.

    Losing 40% of your data to ad blockers. PostHog's reverse proxy setup routes events through your own domain, bypassing most ad blockers.

    Iterating fast on analysis. You frequently create custom dashboards, need to answer ad-hoc questions quickly, and hate waiting for data to "process."

    When PostHog Falls Short

    Don't choose PostHog if you need:

    Real Examples from My Experience

    SaaS Startup (B2B)

    Context: 50k monthly active users, product-led growth, 8-person engineering team.

    Chose PostHog because we needed feature flags for gradual rollouts, session replay to debug customer support issues, and funnels to optimize our onboarding flow. The PMs could write SQL to answer their own questions.

    Cost: ~$500/month vs GA4's free tier, but PostHog replaced 5 separate tools we were evaluating.

    E-commerce Store

    Context: 500k monthly visitors, heavy Google Ads spend, dedicated marketing team.

    Chose GA4 because Google Ads attribution was critical, the marketing team already knew GA, and enhanced e-commerce tracking worked out of the box. The scale was free, and we didn't need product analytics features.

    Healthcare SaaS

    Context: HIPAA compliance required, 20k monthly active users.

    Chose PostHog (self-hosted) because we needed complete data control. Self-hosting on our compliant infrastructure meant no BAA required, no data leaving our servers, and full audit trails for regulators.

    Hybrid Approach

    Context: Product company with a marketing site and SaaS app.

    Chose both: GA4 on the marketing site to track SEO and paid acquisition, PostHog in the app to track feature usage and retention. Best of both worlds, minimal overlap in what each tracks.

    Getting Started: Code Examples

    Setting Up GA4

    GA4 is straightforward—add one script tag and you're tracking pageviews automatically:

    <!-- Add to your <head> -->
<script
  async
  src="https://www.googletagmanager.com/gtag/js?id=G-XXXXXXXXXX"
></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag() {
    dataLayer.push(arguments);
  }
  gtag('js', new Date());
  gtag('config', 'G-XXXXXXXXXX');

  // Custom event tracking
  gtag('event', 'purchase', {
    transaction_id: 'T12345',
    value: 25.99,
    currency: 'USD',
  });
</script>

    The catch: 30-40% of users with ad blockers will block this script, so you'll lose a significant chunk of your data.

    Setting Up PostHog

    PostHog requires slightly more setup, but you get more control:

    // In your Next.js or React app
import posthog from 'posthog-js';

if (typeof window !== 'undefined') {
  posthog.init('phc_XXXXXXXXXXX', {
    api_host: 'https://app.posthog.com', // or your reverse proxy
    autocapture: true,
    session_recording: {
      maskAllInputs: true,
      maskTextSelector: '.sensitive',
    },
  });
}

// Track custom events
posthog.capture('purchase_completed', {
  transaction_id: 'T12345',
  value: 25.99,
  plan: 'pro',
});

// Identify users
posthog.identify('user_123', {
  email: 'user@example.com',
  plan: 'pro',
});

// Check feature flags
if (posthog.isFeatureEnabled('new-dashboard')) {
  // Show new UI
}

    The advantage: With a reverse proxy (routes through your domain), you bypass most ad blockers. Plus, you get feature flags in the same SDK.

    Self-Hosting PostHog

    If you need complete control:

    # Docker Compose setup (simplified)
version: '3'
services:
  posthog:
    image: posthog/posthog:latest
    environment:
      SECRET_KEY: <random-key>
      POSTGRES_HOST: postgres
      CLICKHOUSE_HOST: clickhouse
    depends_on:
      - postgres
      - clickhouse
      - redis

    Self-hosting means no event limits (only bounded by your hardware), complete data ownership, and no vendor lock-in.

    Privacy & Compliance

    Both platforms handle privacy differently, and this matters if you're operating in regulated industries or serving EU users.

    GA4's Approach

    GA4 is compliant, but you're trusting Google's infrastructure and policies. For most businesses, this is perfectly fine.

    PostHog's Approach

    PostHog gives you more flexibility. You can track anonymously without consent, then upgrade to identified tracking when users opt in. If you self-host, you control every aspect of data storage and processing.

    Performance Impact

    Analytics shouldn't slow down your site. Here's what each adds:

    GA4:

    PostHog:

    Both are lightweight enough that performance isn't a deciding factor.

    My Recommendation

    Here's my decision framework:

    Choose GA4 if:

    Choose PostHog if:

    Run both if:

    The Bottom Line

    GA4 and PostHog aren't really competitors—they serve different teams asking different questions.

    GA4 is the right choice for marketing teams who need to track campaigns, optimize ad spend, and understand acquisition funnels.

    PostHog is the right choice for product teams who need to understand how users actually use their product, ship features safely, and iterate fast on insights.

    The best analytics platform is the one your team will actually use to make better decisions. Choose based on who will use it, what questions they need answered, and how much control you need over your data.

    For my projects, I use PostHog for product analytics and feature flags, and I'll add GA4 if I'm running paid acquisition campaigns. That combination gives me everything I need without paying for tools I don't use.