- Google Ads helps you maximise your return on investment (ROI) by showing your ads more often on days when Search traffic is higher.
- When your ads are shown more often, your total daily cost might be up to 2 times your average daily budget, unless you're paying for conversions. If you pay for conversions, your daily costs may be more than 2 times your average daily budget. However, with all Google Ads campaigns you won't be charged more than your average daily budget multiplied by the average number of days in a month (30.4).
Why campaigns might cost more than their average daily budget
For each of your ad campaigns, you'll set an average daily budget — the amount that you've budgeted to spend on your ads each day. If you've noticed that the total daily cost of your campaign is more than your average daily budget amount, that means that your campaign is spending more of your budget on days with higher Search traffic and less on days with lower traffic. Search traffic can fluctuate for several reasons: whether it's the weekend or weekday, or due to seasonality and holidays.
Dipping into your average daily budget for other days in the month helps to optimise the performance of your campaigns and helps make sure that your ads can run a little more on days when they’re very popular.
How you’re charged when campaigns exceed their average daily budget
Up to 2 times your campaign's average daily budget can be used to show your ads on certain days of the week or certain times of the month based on fluctuations in traffic — but not more than you spend on your campaigns each month. For campaigns where you pay for conversions, your daily costs may exceed 2 times your average daily budget.
If your average daily budget is US$10, up to US$20 can be used to show your ads on certain days based on fluctuations in traffic.
Note that sometimes your daily costs might exceed the cap of 2 times your average daily budget. However, you'll still only be charged up to 2 times your average daily budget. For example, if your average daily budget is US$10, and you've accumulated $23 in costs on a given day, you'll only be charged $20 per day. The remaining $3 is returned to you as an overdelivery credit, which you can see in your transaction history.
About the monthly charging limit
While the cost of your campaign can be up to two times your average daily budget on any given day, you won't be charged more than the monthly charging limit that Google Ads uses to prevent you from accidentally getting overcharged. This means that as long as your budget is consistent for an entire month, you won't be charged more than your average daily budget multiplied by the average number of days in a month, which is 30.4 (365 days in a year ÷ 12 months).
If your budget is the same value throughout a month, and you accrue more costs in a calendar month than your monthly limit allows, you'll only be charged your monthly limit. For instance, if your average daily budget is $10 per day throughout a month (a $304 monthly charging limit), and you've accrued $310 in costs over a calendar month, you'll only be charged $304. Here's the maths:
US$10 (average daily budget) x 30.4 (average days per month) = US$304
The other $6 is returned to you as an overdelivery credit.
How budget changes affect the monthly charging limit
When you change your budget, your spend for the rest of the month won’t exceed your new average daily budget multiplied by the remaining days in the month.
For example, let’s say that you have an average daily budget of US$5, and as of 24 November you’ve spent US$113. On the same day, you change your average daily budget to US$10. The maximum you’ll be charged for the month of November will be:
$113 spent so far + ($10/day X 7 days remaining) = $183