Fluctuations in AdSense Earnings

The AdSense earnings can vary from as few as two to three cents per click to as much as one dollar per click. These fluctuations are quite normal and are usually the result of one or more of the following reasons.

• Drop in ad impressions due to reduced traffic or page views
• Drop in the click-through-rate (or CTR) - A CTR of 1% to 4% is considered normal but I have seen days where it drops to as low as 0.5%
• Lack of relevant contextual ads for the content of the pages - low relevancy would mean that AdSense would serve low paying ads
• Reduction in advertising budgets of advertisers
• Seasonal variations - for example, festive seasons may attract bigger advertising budgets and therefore there will be higher cost-per-clicks (CPC)
  

The advertisers seem to bid higher on the beginning and in the middle of a month. But, CPC seem to drop towards the end of the month, probably because advertisers run out of gas.

Further Reading:

• Diagnosing and treating revenue fluctuations (Part I)
• Diagnosing and treating revenue fluctuations (Part II)