The amount you specify as the monthly budget for your SmartAd set will be spent evenly across each month based on Facebook’s pacing algorithm.
Pacing is the control logic that determines how your budget should be spent relative over the current month. Pacing ensures uniform competition throughout the month and automatically allocates budgets to different ads. Pacing is a core part of optimization which ensures that return on investment (ROI) is maximized for the advertisers.
Note: The budget will reset each month as long as SmartAds are enabled. Your daily spending limits through SmartAds will reflect the daily spending limit Facebook has given your ads account.
If you have received a grant or outside funding, it’s important to set your monthly budget to this amount. Anything extra will be charged to the credit card you have on file with Facebook ads.