There have been many complaints in the Google AdSense Help forums from publishers complaining their daily earnings are fluctuating and less than they should be.

The answer to why people are seeing huge differences in the past week or so is because Google AdSense changed how they manage the reporting pipeline.

Google AdSense engineer, Guillaume, said, “since May 14, earnings for the current day reported in the interface may now fluctuate, due to a change in the reporting pipeline.”

Google has a document explaining the issues, saying that now they show gross click counts before they may discount those clicks due to invalid clicks. The document explains it well:

Forum discussion at Google AdSense Help.