A publisher might measure trial starts per offer viewer or purchases per session. Those are different rates. Name the counted action, eligible opportunities and allowed time to convert. (Reuters Institute Digital News Report 2026 ↗ · Google Ads conversion rate definition)
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Counting the action and exposed readers
Illustrative May funnel: 40 of 2,000 unique readers who viewed the same offer during May started a trial within seven days of viewing. That offer-view-to-trial rate is 40 ÷ 2,000 = 2%; all site visits, including people who never saw the offer, are a different denominator.
Give every reader the full conversion window
Give everyone in the example the full seven-day window. A reader who sees the offer on May 31 needs observation through June 7. Closing the report on May 31 gives later viewers less opportunity to convert and can distort the comparison.
Keep the denominator tied to the decision
If 40 of 2,000 offer viewers buy, the rate is 2%. Counting only the readers who clicked checkout would answer a narrower question. Record when people saw the offer and give them the same time to convert before comparing groups.