Google Analytics 4 (GA4): The 2026 Essential Guide

Google Analytics 4 (GA4) is now Google's only analytics platform — the old Universal Analytics (UA) stopped collecting data back in 2023, and its historical data was permanently deleted in mid-2024. If you're still making sense of GA4 with a UA mindset, plenty of things won't line up. This 2026 update takes you through GA4 from scratch: what it is, what's changed over the past couple of years, how to set it up step by step, how to link it to Google Ads, and what Hong Kong advertisers genuinely need to watch out for.

What is GA4?

Quick answer: GA4 is Google's current analytics platform for websites and apps, built around the "event" as its core unit to track user behaviour across devices and platforms, with deep Google Ads integration. It replaced Universal Analytics, which was built around the "session".

GA4 records every interaction a user has on your website or app — page views, scrolls, clicks, downloads, form submissions — and treats them all as "events". From those, you pick the behaviours that matter most to the business, mark them as "key events", and use them to measure performance and bid on your ads.

How is GA4 different from Universal Analytics?

Quick answer: The most fundamental difference is that GA4 measures in "events" while UA measured in "sessions". In GA4 every interaction is an event, which lets it track more flexibly across devices and platforms and suits a privacy-first, machine-learning-assisted era.

In UA, data was organised around sessions and page views; in GA4, everything is events and parameters. That brings far more flexibility, but it also means old metrics (the definition of bounce rate, for one) and the whole report structure work differently — don't drag your UA instincts across wholesale.

What's new in GA4 in 2024–2026?

Quick answer: The biggest change was renaming "Conversions" to "Key events" in March 2024; on top of that, GA4 added AI generated insights, a way to isolate AI assistant referrals via a custom channel group, and a slimmed-down set of attribution models.

"Conversions" renamed to "Key events" (March 2024): Inside GA4 the term is now "Key events", while "Conversion" is reserved for the Google Ads side. This was meant to end years of confusion over "conversion" numbers that never matched between GA4 and Ads (more on that below — and see why conversions look lower in GA4).
AI generated insights and an assistant: The GA4 home now automatically summarises the most important changes in your data since you last logged in (anomalies, seasonality, configuration changes) and offers setup suggestions.
Isolating AI assistant referrals (2026): Referral traffic from AI assistants such as ChatGPT, Gemini and Claude is not yet a native GA4 channel — it still lands in Referral or Organic unless you build a custom channel group (a regex on the referrer) to isolate it. For brands that care about answer engine and generative engine optimisation (AEO/GEO), setting this up is an important step towards measuring how much traffic AI search actually sends you.
Slimmer attribution models: Since November 2023, GA4 keeps only three attribution models (more below).

GA4 setup in six steps (2026)

Quick answer: Basic GA4 setup breaks down into six steps: create the property, set up a web data stream, switch on Enhanced Measurement, mark your key events, link Google Ads, and import those key events into Ads as conversions.

Create the account and property: Go to Admin (the gear icon at the bottom of the left-hand navigation) → Create → Property, fill in the name, reporting time zone and currency, then choose your business category and objectives. ⚠️ Get the time zone and currency right at creation — changing the time zone later does not apply retroactively to past data.
Set up a web data stream: Choose the "Web" platform, enter your site URL and create the stream. You'll get a Measurement ID (format G-XXXXXXXXXX), which you install via the Google tag (gtag.js) or Google Tag Manager (GTM). ⚠️ Never hard-code both a gtag and a GTM GA4 tag at once, or you'll double-count.
Switch on Enhanced Measurement: Enable it in the data stream settings and GA4 will automatically track scrolls, outbound clicks, site search, video engagement, file downloads, and — still a limited/beta signal — form interactions (form_start/form_submit). (Auto-tracking for forms and single-page apps isn't always reliable — verify it in DebugView before you count on it.)
Mark your key events: In Admin → Events, toggle the events that matter to "Mark as key event". Note: marking a key event in GA4 does not by itself send the data to Google Ads — importing is a separate step.
Link GA4 to Google Ads: Create the link in Admin → Product links → Google Ads links, and switch on "Personalised advertising" and "Auto-tagging". Auto-tagging (GCLID) is the prerequisite for importing conversions.
Import key events into Ads as conversions: Import from GA4's Advertising → Conversions, or from Google Ads' Tools → Data manager. ⚠️ Don't track the same conversion via both the GA4 import and a native Ads tag, or you'll double-count — pick one as primary and set the other to secondary.

What's the difference between "key events" and "conversions"?

Quick answer: In 2026's terminology, a "key event" is a GA4-side concept (an important behaviour you mark in GA4) and a "conversion" is a Google Ads-side concept (used for ad measurement and bidding). The flow is: Event → Key event (GA4) → Conversion (Ads).

Put differently, the same important behaviour is called a "key event" in GA4, and once it's imported into Google Ads for measuring ads and driving Smart Bidding, it becomes a "conversion" in Ads. The rename exists precisely to give each platform its own term and cut down on confusion.

How do you link GA4 to Google Ads and import conversions?

Quick answer: Create the link in GA4 under Admin → Product links → Google Ads links, switch on auto-tagging, then import your GA4 key events into Google Ads as conversions — once imported, the action shows up in Ads under "Goals" with a source of "Google Analytics (GA4)".

Once linked, GA4 audiences can be published to Google Ads for remarketing (for example, serving YouTube remarketing ads to those visitors), while key events can serve as the source for conversion tracking that Smart Bidding uses. Keep a single source per conversion to avoid double-counting against a native Ads tag.

Consent Mode v2, first-party mode and server-side tracking: what do Hong Kong advertisers actually need?

Quick answer: Consent Mode v2 is triggered by the user's location and only applies to EEA/UK traffic. If you serve a Hong Kong-only audience, you don't need a GDPR-style cookie consent banner or Consent Mode v2 — but if you run ads into the EEA/UK, you must comply with the rules there.

This is where most Hong Kong advertisers get it wrong, so let's clear it up:

Consent Mode v2 targets EEA/UK users and, since March 2024, is a prerequisite for using Google/Meta advertising audience features. It's triggered by the user's location, not where your company sits — a purely Hong Kong audience isn't affected.
Third-party cookies were not deprecated. Google reversed its plan in 2024; Chrome still keeps cookies by default with no removal timeline. The "cookieless apocalypse" line is out of date.
What is worth doing for every account is Enhanced Conversions and first-party mode. The data loss caused by Safari, Firefox and ad blockers is global and has nothing to do with Chrome — filling the gaps with first-party data is the robust approach.

The three attribution models in 2026

Quick answer: In 2026 GA4 keeps only three attribution models: data-driven attribution (the default), paid and organic last click, and Google paid last click. The old models — first click, linear, time decay, position-based — were removed in November 2023.

If you still see older articles teaching "first click" or "linear" attribution, that's out of date. The 2026 default is data-driven attribution (DDA), which uses machine learning to distribute credit across the touchpoints on a conversion path. To understand the concept in depth, see our essential guide to attribution models.

Common mistakes and a "day-one checklist"

Quick answer: The two most common traps on a new property are that data retention defaults to just two months, and the time zone defaults to US Pacific Time. Fix both on day one, right after creation.

Data retention: The default is only 2 months — change it to 14 (Admin → Data retention), otherwise Explore reports will lack historical data.
Time zone and currency: Set them to Hong Kong (GMT+8) and HKD at creation; time zone changes are not retroactive, though currency changes are. Always attach currency: "HKD" to purchase events, or the revenue goes missing.
Settings that fail silently: an internal-traffic filter left in "Testing", a Search Console collection that was never "Published", a GTM container that was never "Published" — these look done but do nothing at all.
Avoid double-tracking: don't run a hard-coded gtag and a GTM GA4 tag on the same page.

Why do GA4 and Google Ads numbers never match?

Quick answer: Because the two use different "clocks, judges and memory": Google Ads backdates conversions to the click date, counts only its own credit and models more data, so it usually reports higher than GA4; GA4 counts on the actual conversion date and shares credit across channels. A 10–35% gap is normal — compare trends, not single-day figures.

The main reasons:

Timing: Ads counts a conversion on the click date (backdated), while GA4 counts it on the actual conversion date.
Attribution: GA4's data-driven attribution shares credit across every channel, including non-Google ones; Ads only counts credit within its own walls.
Conversion window: Ads defaults to 30 days post-click, while GA4 defaults to 90 days for non-acquisition key events — these should be aligned.
Modelling: Ads models more data (from its vast pool of signed-in users), which is why it usually reports higher.

Understand this and you won't mistake a mismatch for a bug.

Notes for Hong Kong advertisers

Quick answer: Hong Kong's Personal Data (Privacy) Ordinance (PDPO) is not the same as the EU's GDPR — you generally don't need a mandatory cookie consent banner, but if you use cookie data for direct marketing (a remarketing pixel, say), you must obtain explicit opt-in consent.

PDPO ≠ GDPR: For a purely Hong Kong audience, notice and a privacy policy are generally enough — only "direct marketing use" requires explicit consent.
Currency and time zone: Set reporting currency to HKD and time zone to GMT+8; always send HKD amounts on purchase events.
Low-traffic sites: Reports such as demographics may be hidden by a "threshold" — widen the date range and they'll appear.

Conclusion

GA4 is no longer just a reporting tool; it's Google's event-first, AI-assisted measurement platform. Get "key events vs conversions" straight, link Google Ads correctly, dodge the time zone and data retention default traps, and understand that Hong Kong doesn't actually need the EU's cookie-consent playbook — and you'll give your ad decisions a reliable data foundation.

If your GA4 numbers never match Google Ads, that gap is by design — here is why GA4 shows fewer conversions.

FAQ

What is GA4? GA4 (Google Analytics 4) is Google's current analytics platform, built around the "event" to track user behaviour across devices and platforms, with deep Google Ads integration. It replaced Universal Analytics in 2023.

What's the difference between GA4's "key events" and "conversions"? A "key event" is a GA4-side concept (an important behaviour you mark), and a "conversion" is a Google Ads-side concept (used for ad measurement and bidding). The flow is: Event → Key event (GA4) → Conversion (Ads).

How do I link GA4 to Google Ads? In GA4, go to Admin → Product links → Google Ads links to create the link, switch on personalised advertising and auto-tagging, then import your key events into Google Ads as conversions.

Why don't GA4 and Google Ads conversion numbers match? Because they count differently: Ads backdates to the click date, counts only its own credit and models more, so it usually reports higher; GA4 counts on the actual conversion date and shares credit across channels. A 10–35% gap is normal — compare trends.

Do I need a cookie consent banner or Consent Mode v2 for GA4 in Hong Kong? Generally no. Consent Mode v2 is triggered by the user's location and only applies to EEA/UK traffic; a purely Hong Kong audience isn't affected. But if you run ads into the EEA/UK, you must comply with the rules there.

How long should GA4 data retention be? Change it from the default 2 months to 14 months (Admin → Data retention), so you keep enough historical data for Explore reports.

Running Google Ads in Hong Kong or Malaysia and not sure your tracking is telling you the truth? Get a free Paid Media Health Check — no sales pitch, just honest findings on your GA4 and Google Ads setup.