Since 4 October, Google changed the overdelivery on Daily Budget of Adwords, that now can reach 2 times more the daily budget. Before this change, the limit was around 20%. Now, if advertisers overdelivery the daily budget in one-month billing cycle, Google will credit the overdelivery. Google wants that advertisers see more performance, that many times is constrained by daily budgets.
Google says this change will allow more performance on the advertising goals, like clicks and conversions. And explains: “on days with lots of high-quality traffic, the costs could be up to 2 times your daily budget. This spending is balanced by days when your spend is below your daily budget.”
Google is giving more importance to the monthly budget than the daily budget: “over a month-long billing cycle, you won’t be charged more than your daily budget would’ve allowed for over 30.4 days. 30.4 is the average number of days in a month (365 days in a year / 12 months = 30.417). Google multiplies your daily budget by this number so we know what your budget should be over the course of a month.”
Here an example from Google: “your budget at $5 a day and your billing cycle is 30 days. Over the course of the month, you notice that your charges vary. Some days you’re charged $2, on others you’re charged $10. But at the end of the month, your charges won’t exceed $152 (that’s 30.4 multiplied by your $5 budget).”
PPC Hero wrote here a guide how to check the overdelivery on Adwords Beta.