How are Campaign analytics calculated?

Smart Notification Overview

On the Campaign tab, the Overview section displays the total number of messages sent from your Campaigns in the past 90 days. Additionally, aggregate statistics like open rate and spam rate of your email messages are calculated by taking the total number of messages that were opened for all messages listed in your Campaigns and dividing that by the total number of messages that were sent from your Campaigns, over the most recent 90 days.

For more information on how Campaign analytics are calculated, see this additional help article on how message analytics work.