The daily budget is the average daily amount you are willing to spend on each campaign over a calendar month. For example, if you set your daily budget to $100, Amazon.com will deliver up to $3,100 worth of clicks in that calendar month, assuming you start your campaign on the first day of a 31-day month.
Calculating your average daily budget
You can calculate your average daily budget by following these steps:
Decide how much you are willing to spend on your Sponsored Products campaign for a month. For example, let's say your monthly budget is $3,100.
Calculate your average daily budget by dividing your total budget of $3,100 by 31 days. Your average daily budget would be about $100.
You can change your budget at any time. From the Manage Advertising view, simply click the budget amount in the Daily Budget column and enter a new amount. You can also change the daily budget by clicking the campaign name and selecting the Campaign Settings tab.
Account Daily Budget Cap
The Account Daily Budget Cap is an optional setting that governs how much, in aggregate, all of your active campaigns can spend per day. You can set or change your Account Daily Budget Cap by selecting the Advertising Settings tab in Campaign Manager. For example, you have two campaigns each with a daily budget of $50. If you set an account daily budget of $75, then your ads will stop displaying once your total account spend reaches $75, even though the total budget for your two campaigns is $100.
If you are not sure what to set for an account level budget, then you can leave this blank and simply use the budgets set for each campaign.