When someone clicks your ad, the actual amount you’re charged will be

• The minimum needed to hold your ad position, under the maximum cost-per-click limit
• The minimum needed to hold your ad position or 50% of your maximum cost-per-click bid, whichever is greater
• The minimum needed to hold your ad position but never more than 120% of your maximum cost-per-click bid, whichever is greater
• The minimum needed to hold your ad position but never less than 50% of your maximum cost-per-click bid, whichever is greater