When someone clicks your ad, the actual amount you’re charged will be:
The minimum needed to hold your ad position or 50% of your maximum cost-per-click (max. CPC) bid, whichever is greater
The minimum needed to hold your ad position but never less than 50% of your maximum cost-per-click (max. CPC) bid, whichever is greater
The minimum needed to hold your ad position but never more than 120% of your maximum cost-per-click (max. CPC) bid, whichever is greater
The minimum needed to hold your ad position, under the maximum cost–per–click (max. CPC) limit
Explanations:
Your actual cost per click (actual CPC) is the final amount that you’re charged for a click. You’re often charged less – sometimes much less – than your maximum cost-per-click (max. CPC) bid, which is the most you’ll typically be charged for a click.Actual CPC is often less than max. CPC because, with the AdWords auction, the most that you’ll pay is what’s minimally required to hold your ad position and any ad formats that are shown with your ad, such as sitelinks.
Actual CPC is often less than max. CPC because with the AdWords auction, the most you’ll pay is what’s minimally required to hold your ad position and any ad formats shown with your ad, such as sitelinks.
Read more here: https://support.google.com/adwords/answer/6297?hl=en
