Summary
Transaction IDs are the unique purchase identifier that should be shared to prevent conversion duplication and support value-based bidding. Google Ads uses the transaction ID to recognise repeat reports of the same order and count it once, which keeps the revenue signal clean for Target ROAS and Maximise Conversion Value. The same ID is also required later if you need to upload refunds or corrected conversion values.
Nitin Batra is a Google Ads Search certified professional who implements purchase conversion tracking with transaction IDs and manages value-based bidding strategies on live ecommerce accounts.
Last updated: August 22, 2026
To prevent conversion duplication and support value-based bidding, share Transaction IDs, the unique order identifier passed with every purchase conversion so Google Ads counts each sale once and attributes the correct revenue value.
- Ad group ID
- User IP address
- Browser type
- Transaction IDs
The correct answer is: Transaction IDs
Key Takeaways
- – Transaction IDs are the unique purchase identifier that should be shared to prevent conversion duplication and support value-based bidding.
- – The transaction_id parameter is passed with the purchase event through the Google Ads tag, Google Tag Manager or an offline conversion import, and Google Ads deduplicates any purchases sharing the same ID.
- – Value-based bidding strategies like Target ROAS and Maximise Conversion Value optimise against reported revenue, so inflated or duplicated values push the algorithm to bid on the wrong auctions.
- – Transaction IDs are also the matching key for conversion adjustments, so refunds, cancellations and corrected order values cannot be uploaded if the ID was never sent in the first place.
Where do I pass the transaction ID in a Google Ads purchase conversion?
It goes in the transaction_id field of the conversion event, either in the gtag purchase snippet on the order confirmation page or as a mapped variable in the Google Ads Conversion Tracking tag inside Google Tag Manager. Most ecommerce platforms already push the order number into the data layer, so you map that data layer variable to transaction_id. You can verify it is firing using Tag Assistant on a live test order.
What actually causes duplicate purchase conversions?
The most common causes are customers refreshing or bookmarking the thank you page, the tag firing twice because it is hardcoded on the site and also deployed through Tag Manager, and the same order being counted by both website tracking and an offline import from your CRM. Sending a consistent transaction ID in all cases lets Google Ads collapse them into a single conversion. Without it, every page load is treated as a fresh sale.
Do ad group ID, user IP address or browser type help with deduplication?
No. Ad group ID tells you where the click came from, not which order was placed. IP address and browser type are session level signals that are not unique to a purchase, and multiple orders can share the same IP or browser fingerprint. Only the transaction ID is guaranteed unique per order, which is why it is the deduplication key.
Can I fix a conversion value after the sale if I did not send a transaction ID?
No, and this is the mistake that costs advertisers the most. Conversion adjustments for refunds, cancellations or corrected order values are matched using the transaction ID plus the original conversion time, so if the ID was never sent, there is nothing to match against. Set it up before you switch to Target ROAS, not after you notice the revenue numbers are wrong.