GA4 key events or Google Ads conversions: what Smart Bidding should optimise towards

Open the conversion actions list in an inherited Google Ads account and you very often find the same picture: purchases tracked with the Google Ads tag, the same purchases imported from GA4, a couple of scroll events and a few page views promoted to "conversion" years ago. All of them primary. Nobody is quite sure any more which number Smart Bidding is looking at — and Smart Bidding, meanwhile, is optimising towards exactly that mix.

This article is about putting things in order: what GA4 key events are today, when it makes sense to import them into Google Ads and when to use the native tag, the configuration mistakes we see most often, and how to check in half an hour what your campaigns are really optimising towards.

From "conversions" to "key events": what changed in 2024

In March 2024 Google renamed GA4 "conversions" to key events. The way events are collected did not change: the vocabulary did, and it is useful vocabulary because it separates two things that used to blur together.

• Key event: an action you consider important in GA4 — a purchase, a form submission, but also a download or a visit to the pricing page. It is there to analyse behaviour. According to Google’s documentation, key event metrics are aggregated in Analytics reports and are not directly eligible for bidding.
• Conversion: an action you use to measure campaigns and optimise bidding in Google Ads. It can come from the Google Ads tag or from an imported GA4 key event. Only conversions are eligible for bidding and reporting in Google Ads.

The sequence, as Google describes it, is event → key event → conversion. The practical consequence is simple: marking an event as "key" in GA4 is an analysis decision, and a low-risk one. Making it a primary conversion in Google Ads is a budget decision.

Google Ads tag or GA4 import: the two routes

There are two ways to measure a purchase or a lead in Google Ads. The first is a website conversion action fed by the Google tag (directly or through Google Tag Manager) with a Google Ads conversion ID and label. The second is a conversion created from a key event in a linked GA4 property. They often rely on the same Google tag on the site, but they reach different numbers because they attribute, count and transmit data differently.

Attribution is the difference that matters most

In GA4 you choose which channels can receive credit for web conversions shared with Google Ads: Google paid channels only, or paid and organic channels. In the second case, if someone clicks an ad, comes back a week later from an organic search and buys, GA4 may give organic some or all of the credit — and Google Ads receives a fraction of a conversion, or nothing. That is the right behaviour if you want to stop Google Ads claiming credit it has not earned; it is a problem if you do not know it is happening and compare that figure with the native tag’s. Changing the setting only applies from that point forward. Why the two systems will never match whatever you choose is covered in our piece on data-driven attribution across Google Ads and GA4.

Lag weighs on bidding

Smart Bidding works on recent data. A conversion that reaches Google Ads a day after it happened is a conversion the algorithm cannot see when it sets that day’s bids. On high-volume accounts the difference is absorbed; on accounts with a handful of conversions a day it can make target CPA or ROAS strategies jumpier.

Enhanced conversions and modelling

Enhanced conversions improve measurement by matching hashed first-party data. On the native tag they are switched on through the Google tag and, during 2026, Google is merging the web and leads variants into a single setting: the details are in our article on enhanced conversions for leads and the Data Manager API. For conversions imported from GA4, Google Ads enhanced conversions do not apply: the route there is user-provided data collection in Analytics. In September 2026 Google announced the launch of enhanced conversions in Analytics as well; at the time of writing, check in your own property what is already available.

Primary actions, secondary actions and goals

In Google Ads, conversion actions are grouped into goals (purchases, leads, contacts and so on). Three rules decide what Smart Bidding uses:

1. Account-default goals. If a goal is set as account default, its primary actions are used for reporting and bidding in every campaign that does not have campaign-specific goals.
2. Primary or secondary action. Primary actions feed the "Conversions" column and drive bidding. Secondary actions are for observation: you see them in "All conversions", but as a rule they do not influence bidding.
3. Campaign-specific goals. A campaign can override the account goals and use others. Watch out for custom goals: they can include secondary actions too, which are then used for bidding in the campaign the goal is assigned to.

Rule 3 is the one that slips through quick checks: "it is secondary, so it does not count" is only true until someone builds a custom goal that includes it.

The classic mistake: the same purchase counted twice

The scenario we find most often in ecommerce accounts: a "Purchase" action from the Google Ads tag and a "purchase" action imported from GA4, both primary in the same account-default goal. Google Ads does not deduplicate across different conversion actions, so every order attributed to ads is counted twice (or once plus a fraction, depending on GA4 attribution).

The consequences go beyond an inflated report. An illustrative example: 100 real orders become 200 conversions, CPA looks halved and ROAS doubled. A 400% target ROAS is "met" while the real ROAS is around 200%, and the algorithm keeps pushing bids that, on the true numbers, do not stack up.

The fix is easy to state: one primary action per business outcome, the other secondary. Two precautions are essential, though:

• Do not delete the excluded action straight away. Leave it as secondary: you will want it to compare figures over the following weeks.
• Recalibrate your targets. When you remove double counting, reported ROAS halves overnight. Leave the target ROAS at its old, inflated level and the campaign will throttle sharply. Reset the target to values consistent with the new count, and warn whoever reads the reports beforehand.

"One" or "Every": counting

For each action Google Ads asks whether to count every conversion after an ad interaction or only one. The logic is the one Google sets out: "Every" for purchases, bookings and subscriptions, where each event has value; "One" for forms, calls and sign-ups, where the same person submitting twice is not a second customer. In Google’s own example, a click that leads to two sales and two leads produces three conversions: two sales and one unique lead.

With GA4 imports there is an extra layer: the key event has its own counting method too, "once per event" (the one Google recommends) or "once per session". A lead form imported with "once per event" counts every reload of the thank-you page and every double submission. The rule is to align the two layers and check them together, not one at a time.

Micro-conversions promoted to primary

A 90% scroll, a page_view on a specific page, a click on the phone number with no minimum call length, a video start: useful events in GA4, terrible primary actions. Smart Bidding does exactly what you ask, which is to find the people who complete that action at the lowest cost. If the action is a scroll, it will buy traffic that scrolls, and the "conversion" count will climb while leads and sales stay flat. Campaigns with broad inventory, such as Performance Max and Demand Gen, are the quickest to find these shortcuts.

Micro-conversions make sense as secondary actions, to understand behaviour. In accounts with very few conversions you can temporarily use an intermediate event as primary, but only if it is genuinely correlated with sales, with a proportionate value and a date by which you return to the real goal.

How to check what Smart Bidding is really optimising towards

This is the first check we run on every account we take over. It takes about half an hour and no external tools:

1. List the conversion actions with source, status and primary/secondary. Look for the same outcome measured twice, for example a purchase from the website and one from Google Analytics.
2. Check which goals are account defaults and which primary actions they contain.
3. Open each campaign’s settings and see whether it uses account goals or campaign-specific ones, custom goals included.
4. Segment the "Conversions" column by conversion action, campaign by campaign: it is the exact picture of what feeds bidding.
5. Check counting, window, model and value on every primary action; for GA4 ones, check the counting method and attribution settings in the property as well.
6. Compare with your back office or CRM: real orders or leads for a week against conversions by conversion time. There is always some gap; a ratio close to 2:1 is almost always double counting.
7. Read the change history: edits made in GA4 to imported conversions only show up there.

If the check reveals that tracking was broken, inflated or missing for a period, data exclusions exist precisely to tell Smart Bidding to ignore those days. This check is also the first block of our account audit checklist.

How we set it up

• A single primary action per business outcome, usually from the Google Ads tag with enhanced conversions switched on. For lead generation, ideally fed by the real outcome in the CRM.
• The equivalent GA4 key event imported as secondary, so the same number is visible in GA4 and Google Ads and you have a point of comparison.
• GA4 as primary only by choice: in small accounts with no technical access to the site and an already reliable GA4, it can be the cleanest option. What matters is that it is the only primary for that outcome.
• Micro-conversions always secondary, unless there is an explicit, temporary decision.
• Every change to goals and primary actions logged, with date and reason, because it changes what the algorithm learns.

If you are not sure what the "Conversions" column in your account is actually counting, our free audit starts right there: actions, goals, counting and consistency with your real sales data. You can see how we work and find more answers in the FAQ.