If like most webmasters and bloggers you use Google Adsense, it is very important to optimize your Adsense earnings by understanding them. You need to understand page impressions, click-through rate, and cost per click as they all work together to affect your income. I use a free Adsense Calculator that returns estimates of daily, monthly, and yearly earnings and clicks. This is a very helpful tool in deciding whether you even want to use Adsense or not.