Google Ads lets you set an average daily budget for your campaigns, with the flexibility to change it at any time. Your daily budget is the average amount you’d like to spend each day over the course of the month.

While your spend may vary each day, you won’t pay more than your monthly charging limit, which is the daily budget you set, multiplied by the average number of days in a month. On days when your ads are likely to get you more traffic, you may spend up to 2 times your average daily budget. Those days are balanced by days when your spend is below your daily budget.

If you’re creating a campaign with a specific start and end date, you can also set a total budget for the entire duration of the campaign. Campaign total budgets are currently available for video campaigns only.

This article explains how to decide on your daily budget, when to use a campaign total budget, and how budget changes take effect.

How to decide on a daily budget

With Google Ads, you choose a daily budget for each campaign based on your advertising goals and the general amount you're comfortable spending each day.

When to use a campaign total budget

When you already know how much you’d like to spend on your entire campaign, you can set a campaign total budget. Currently, campaign total budgets are only available for video campaigns with a specific start and end date. 

You’ll have the option to select “Campaign total budget” when you create a new video campaign. Keep in mind that you can’t change the budget type once a campaign is created. 

Google Ads will try to spend your total budget evenly over the duration of your campaign while taking into account higher and lower traffic days to optimize your campaign’s performance. For example, let’s say your video campaign gets fewer views on Mondays and Tuesdays and more views on weekends. Google Ads will optimize performance by spending more on days when your video is likely to get more views, while keeping your overall budget goals on track.

With a campaign total budget, you’ll only be billed up to the amount you enter for a campaign, even if Google Ads serves more views or impressions than your budget allows.

How budget changes take effect

When you change your daily campaign budget you'll see these adjustments immediately in your account. Based on when you edit your budget, the way that your campaign spends your budget can vary. Here's what happens to your budget based on the time or frequency of your change:

Mid-day	Campaigns will typically spend around 50% of their budget in the day's first half and the remainder in the day's second half. However, if demand for your ads happens to be greatest early in the day, you might spend 70% of your daily budget in the morning. If you made a budget change around noon, you might spend an additional 50% of your new daily budget in the afternoon, which could result in a total spend for the day which is slightly greater than either of the daily budgets which were in effect that day. This results from the fact that the system is designed to make up for low traffic days by slightly exceeding your daily budget on higher traffic days, as long we never exceed your monthly charging limit. Learn more about Why costs might exceed your average daily budget. If you've lowered your daily budget significantly, it's also possible that your ad distribution will slow significantly for the rest of the day.
Multiple times a day	You'll be charged based on the highest daily budget that you chose for that day.
Mid-month	When you change your budget during the month, 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 you have a daily budget of US$5, and as of November 24 you’ve spent US$113. On the same day, you change your 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
Multiple times a month	The same calculation applies as the one for changing your budget mid-month.

* Nguồn: Google