Choose Google Analytics 4 if your main questions are about marketing: where visitors come from, which campaigns convert, and what to feed back to Google Ads. Choose PostHog if your main questions are about the product: what signed-up users do, which features they adopt, and where they get stuck, with session replay and the option to keep data in the EU or on your own servers.
For most SaaS companies we work with, the honest answer is both: GA4 for acquisition, PostHog for product, joined by the same user ID. This guide explains the differences that matter and how to decide.
What is the difference between GA4 and PostHog?
GA4 is Google’s web and app analytics. It is built around traffic sources, sessions, campaigns and key events, and it connects natively to Google Ads, Search Console and BigQuery. The standard version is free. Its strength is answering “which marketing works?”
PostHog is an open-source product analytics platform that bundles several tools in one: product analytics, web analytics, session replay, heatmaps, feature flags, experiments and surveys. It follows identified users through your product. Its strength is answering “what do our users actually do, and why?”
How do GA4 and PostHog compare feature by feature?
| GA4 | PostHog | |
|---|---|---|
| Main purpose | Marketing and traffic analytics | Product analytics and experimentation |
| Traffic sources and campaigns | Strong, with Google Ads integration | Basic web analytics, improving |
| Event tracking | Automatic events plus custom events | Autocapture plus custom events |
| Per-user journeys | Limited (User Explorer, explorations) | Strong: person profiles and full event history |
| Funnels and retention | Funnel and cohort explorations | Funnels, retention, paths and stickiness |
| Session replay and heatmaps | Not included | Included |
| Feature flags and A/B tests | Not included | Included |
| Hosting | Google’s cloud only | PostHog Cloud (US or EU) or self-hosted |
| Raw data access | BigQuery export | SQL access and data exports |
| Price | Free; GA4 360 for enterprises | Free monthly allowance, then usage-based |
Which is better for marketing attribution?
GA4. It knows your Google Ads clicks, imports campaign costs from Google products, shares key events with Google Ads for bidding, and builds audiences for remarketing. If paid search is a meaningful channel, you want GA4 (or at least Google Ads conversion tracking) in place regardless of what else you use.
PostHog can record UTM parameters and referrers, and its web analytics covers the basics. But it doesn’t feed Google’s bidding algorithms, and that feedback loop is usually worth more than any report.
Which is better for product analytics?
PostHog. Once someone signs up, GA4 struggles: it isn’t built to show one customer’s full history, flexible cohorts are limited, and data thresholds can hide small segments. PostHog is designed for exactly this: identify the user, then analyse what they and their company do over weeks and months.
Session replay is the practical difference most teams notice. Watching ten recordings of people dropping out of onboarding often explains a funnel faster than any chart. For TMT Finance, product analytics and UX forensics on the application journey were what showed why $4,200 of ad spend had produced two conversions; once the onboarding was fixed and Google Ads relaunched, cost per lead fell from $2,140 to $48.74 (read the case).
Which is better for privacy and GDPR?
PostHog gives you more control. You can host your data in PostHog’s EU cloud or run PostHog yourself, and you decide what is captured and for how long. That makes data processing agreements and data-location questions easier to answer.
GA4 can be used compliantly, but it takes work: Consent Mode set up properly, a consent banner that is respected, no personal data in events, and sensible retention settings. Data goes to Google either way. We cover the details in GA4 and data privacy, and server-side tagging gives you more control over what reaches Google; see our server-side Google Tag Manager guide.
Neither tool makes you compliant by itself. Consent, purpose and documentation are still your job.
Is PostHog harder to set up than GA4?
Not really for the cloud version. Both start with a snippet or SDK, and PostHog’s autocapture collects clicks and pageviews without configuration. Self-hosting is a different matter: it means running and upgrading the infrastructure yourself, and PostHog itself steers most companies to its cloud.
The real effort, in both tools, is the event plan: deciding which few actions matter, naming them consistently, and identifying users at sign-up and login. Skip that and both tools produce lots of data and few answers.
What does each tool cost?
GA4’s standard version is free; Google Analytics 360 is the paid enterprise tier with higher limits and support. The BigQuery export is free to switch on, but BigQuery itself is billed by Google Cloud by usage.
PostHog has a free monthly allowance per product (events, recordings, flag requests) and then charges by usage, with each product billed separately. Check PostHog’s pricing page for current limits; costs rise with traffic, so set billing limits from day one.
Can you use GA4 and PostHog together?
Yes, and that is what we usually recommend for SaaS. A common split:
- GA4 on the marketing site and sign-up flow, sending key events to Google Ads.
- PostHog in the product, from sign-up onward, with session replay and feature flags.
- The same user ID in both, set at sign-up and login, so you can connect the campaign that brought a user to what they did afterwards.
- One source of truth for revenue, usually the CRM or billing system, with offline conversions sent back to the ad platforms.
If you are weighing other options, we compare GA4 with Mixpanel and with Matomo too.
FAQ
Is PostHog a replacement for Google Analytics?
For some companies, yes: a product-led SaaS with little paid search can run on PostHog alone. If you spend on Google Ads, keep GA4 or Google Ads conversion tracking, because PostHog doesn’t feed Google’s bidding.
Is PostHog free?
PostHog has a free monthly allowance for each product and an open-source codebase. Beyond the allowance, cloud pricing is usage-based. Self-hosting avoids PostHog’s fees but adds your own infrastructure and maintenance costs.
Does GA4 have session recordings or heatmaps?
No. Teams that need them pair GA4 with a separate tool, or use PostHog, which includes both.
Which is better for a privacy-focused website?
PostHog, because you can choose EU hosting or self-host and control exactly what is captured. GA4 can be configured carefully, but data still goes to Google.
Our analytics team sets up GA4, PostHog and Mixpanel, and connects them; get in touch if you want help choosing.
