What they fix
If a tag broke and conversions went unrecorded for a few days, Smart Bidding would otherwise learn from that false dip and pull back. A data exclusion tells Google to disregard that window so the artifact does not distort bids.
Use them narrowly
Data exclusions are only for genuine measurement failures, and Google advises keeping them short. Do not use them to paper over real performance drops. They are usually set after the fact, the counterpart to seasonality adjustments, which prepare bidding for a known future spike.
Common questions
When should you use a data exclusion?
Only when conversion tracking genuinely failed for a period, so Smart Bidding should ignore that window. Not for real performance dips, and kept as short as possible.
What is the difference between data exclusions and seasonality adjustments?
Data exclusions tell bidding to ignore a past period of broken tracking; seasonality adjustments prepare bidding for an expected future change in conversion rate.
How do you add a data exclusion in Google Ads?
Go to Tools, then Adjustments, open the Exclusions tab and select the plus button. Name it, set the start and end date and time, choose campaigns or the whole account and the affected devices, then save. Exclusions work on clicks, so Google says to cover your conversion delay and exclude at least 90% of affected clicks. They're available for Search, Display, Shopping and Performance Max.