How to measure conversions with GA4 and Google Tag Manager while respecting consent

If you don't know which channel brings you customers, every marketing decision is a gamble. And yet many websites have only half-finished analytics: events nobody remembers creating, conversions counted twice or tags that load before the user accepts cookies.

In this article we go through how to plan conversion measurement with Google Analytics 4 (GA4) and Google Tag Manager (GTM) in an orderly, privacy-respecting way.

Step 1: write a measurement plan

Before configuring anything, write down what you want to measure and why. A simple measurement plan includes:

• Business goals: for example, getting qualified quote requests.
• Key actions: submitting the form, clicking the phone number or WhatsApp, booking a call.
• Useful parameters: form type, service of interest, button location.
• What will not be measured: personal data such as names, emails or phone numbers must never be sent to analytics tools.

This document prevents purposeless events from piling up and makes the reports easy for anyone to understand.

Step 2: define an event naming scheme

GA4 has recommended events with standard names. Whenever one exists, use it. For lead generation, the most important is generate_lead. A common scheme would be:

• form_start: the user starts filling in a form.
• form_submit: they try to submit it after passing validation.
• generate_lead: the server confirms the request has been saved.
• contact_click, whatsapp_click or booking_click: clicks on other contact channels.

The difference between form_submit and generate_lead matters: the first measures attempts; the second, real leads. Only generate_lead should be marked as a key event.

Step 3: centralise tags in Google Tag Manager

GTM lets you manage all tags (GA4, Google Ads, Meta, TikTok…) from one place. The website only has to send events to the data layer (dataLayer), and in GTM you decide which tag fires on each event.

Advantages of this approach:

• A single point of control and less code on the website.
• Tag changes without having to redeploy the website.
• Less risk of the same conversion being sent from two places.

If you use GTM, don't also install the same tags directly in the website's code: it's one of the most common causes of duplicate conversions.

Step 4: set up consent

In the European Union, prior user consent is required to set cookies that aren't strictly necessary, such as analytics or advertising cookies. And rejecting them must be as easy as accepting them.

Google Consent Mode lets Google tags adjust their behaviour to the user's choice. Broadly speaking:

1. When the page loads, permissions are set to “denied” by default.
2. When the user makes a choice in the cookie banner, analytics and advertising permissions are updated.
3. Tags respect those permissions.

There are two ways to implement it. In the basic implementation, tags don't load until there is consent. In the advanced one, they load from the start with denied permissions and send limited, cookieless signals. Choose the approach with your legal adviser: the basic one is the most conservative.

Step 5: check that everything works

Before signing off the measurement:

• Use GTM preview mode and the GA4 DebugView to see which events are sent.
• Test the full journey: reject cookies, accept analytics only, accept everything.
• Submit a test form and check that exactly one generate_lead arrives.
• Verify that no parameter contains personal data.

Step 6: connect analytics with the business

Website analytics counts leads, not customers. To close the loop, store the visit's source alongside each lead (for example UTM parameters or the click ID) and record in your CRM which leads turn into sales. With that information you can compare channels by the value they bring, not just by volume.

Summary

Good measurement rests on a clear plan, a few well-defined events, a single source of tags and properly implemented consent. It isn't the most glamorous part of marketing, but without it everything else is decided blind.

If you'd like to review your measurement, we do it as part of our conversion optimisation and analytics service.

Last updated: 26 October 2026. Questions about this topic? Write to us.