Is the ROI Calculator reporting 100% accurate?

While we wish the answer were yes, the reality is that some recipients may have their browser, proxy server or networking settings configured to block 3rd-party cookies. As a result there would not be a way for our system to receive any data past the initial click-through. 

This behavior would be similar to a recipient who has their email client set to block all images, as this would prevent the "Open" statistic from being logged for your campaign.

As is the case with the Open tracking, it is our recommendation that you use the ROI Calculator as "one of many" variables included in the analysis of your campaign performance.