Why it happens
Two tags send the same purchase. The Google & YouTube sales channel sends a purchase conversion. A Google Ads tag in the theme, in Google Tag Manager or in a custom pixel can send another. Each one fires on the same order, so Google Ads gets two conversions. This often happens after a store moves to a new tracking setup and the old tag stays behind.
Two purchase conversion actions are set as Primary. Google Ads puts only Primary actions in the Conversions column, and bids on them. If the account has a purchase action from the sales channel and a second one imported from Google Analytics, and both are Primary, the same sale can appear in Conversions twice. Google's own help says it sets actions based on Google Analytics key events to Secondary for this reason: "to prevent counting the same event twice for bidding".
The tag sends no transaction ID. Google Ads uses the transaction ID to spot a repeat. Google's help says that if two conversions for the same conversion action carry the same transaction ID, "Google Ads will know the second conversion is a duplicate". Without an ID, a second copy looks like a new sale. Google also says that an ID starting with GG_ was made by Google because your tag did not send one.
The thank you page fires again. A buyer who reloads the order status page, or opens it again from the confirmation e-mail, can fire the purchase tag a second time. With a unique transaction ID, Google drops the repeat. Without one, it counts it. Purchase fires again when the order page is reopened covers this case.
The count setting is set to Every, and that is correct. Google Ads offers two counting options. Every conversion counts each conversion after an ad click, and Google calls it a good choice for sales. One conversion counts only one per click, and Google suggests it for leads. Every is the right setting for purchases. It only inflates the number when the same order arrives twice.
Check it yourself
- 1In Google Ads, open Goals > Conversions > Summary. Look at every action in the Purchase category and note which ones are Primary. A store usually needs one Primary purchase action.
- 2For each purchase action, look at its source. A Website action comes from a tag or the sales channel. A Google Analytics action is imported from GA4. If you see both as Primary, that is the likely cause.
- 3In your Shopify admin, open Sales channels > Google & YouTube > Settings and see whether the channel measures Checkout completed in your Google Ads account.
- 4Search your theme code, Google Tag Manager and Customer events in Shopify settings for a second Google Ads conversion tag, often with an AW- ID and a conversion label.
- 5Open the Diagnostics tab of your purchase action. Google flags "Google tag is missing transaction ID" when your tag does not pass its own ID.
- 6In Campaigns, add the segment Conversions > Conversion action and compare one full week. If two purchase actions both show roughly your order count, you have your answer.
- 7To compare with Shopify, use the column All conv. (by conv. time). Google's help says it reports conversions by the time they happened, not by the date of the ad click, which makes it closer to a list of orders.
When you remove a duplicate, remove it from one place only. Google Ads still needs one source of purchases, or the count falls to zero. If the double count started when you changed tracking apps, see duplicate purchases after switching tracking apps. If you have the opposite problem, with fewer conversions than orders, read Google Ads purchases vs Shopify orders.
FAQ
Should I switch the count setting to One to fix it?
No. One conversion counts one per ad click, so a buyer who orders twice after one click shows as one sale. It hides the duplicate and also hides real repeat orders. Fix the second source instead.
Why does GA4 show fewer purchases than Google Ads?
GA4 gets the purchase once, from its own tag. Google Ads can get it from two tags, or count a GA4 import next to its own action. The two also date sales differently: Google Ads by the day of the click, GA4 by the day of the purchase.
Will a duplicate hurt my campaigns?
It can. Smart Bidding learns from the Conversions column. If each sale counts twice there, your cost per purchase looks half as high as it is, and your return on ad spend looks better than it is.
Does the Secondary setting stop double counting?
For bidding, yes. A Secondary action stays out of the Conversions column and out of bidding, but it still shows in All conversions. One exception: if you add a Secondary action to a custom goal, Google Ads bids on it there.
How do I know which source to keep?
Keep the one that reaches Google Ads with the order's value, currency and a unique transaction ID, and that your team can maintain. Remove or set to Secondary the others.