Max CPC is the highest amount an advertiser is willing to pay for a click on their ad. It is set by the advertiser and is used by the advertising platform, such as Google Ads, Microsoft Ads or Meta Ads, to determine when and where the ad will be shown. The Max CPC is usually set at the keyword level and is an important factor in determining ad rank and placement.

Actual CPC, on the other hand, is the amount an advertiser actually pays when someone clicks on their ad. It is the result of a real-time auction that takes place when someone searches for a keyword or phrase that triggers an advertiser's ad to be shown. The advertiser with the highest ad rank and the most relevant ad typically wins the auction and pays the second-highest bid amount or the minimum necessary to maintain their position.

In most cases, the actual CPC is lower than the Max CPC. There are many factors that determine the actual CPC, such as the level of competition for the keyword, the relevance of the ad and landing page, the ad format, and the bidding strategy. However, in some cases, the actual CPC can also be higher than the Max CPC (for example if you use bid adjustments to increase your Max CPC by a certain percentage in a dynamic fashion to keep up with the competition).

In summary, Max CPC is the highest bid amount an advertiser is willing to pay, while actual CPC is the amount they actually pay when someone clicks on their ad. The actual CPC can be lower than the Max CPC, depending on the competition, relevance, and bidding strategy.