If your ad account doesn't have a billing threshold, we'll charge you up to once a day for ads that you run. For smaller campaigns, we'll wait until the charges amount to GBP 25 or until seven days pass before we invoice your account to avoid frequent charges to your payment method. This may result in a delay in receiving your billing receipt.

Facebook's billable day is on a 24-hour period and not on a calendar-day basis. Facebook ads start running once the ads are approved on your chosen start date. Then they'll stop running at 11:59 pm on your chosen end date.

For example, if your campaign is set to run from 1 January at 9:00 am to 2 January at 9:00 pm with a daily budget of GBP 10, you may be charged up to GBP 15 worth of ads for this campaign because your end date runs past a 24-hour period.

* Nguồn: Facebook