Billing & Budget Explaination:  I hope that this information clarifies any questions that you had concerning this.

Billing Overview:

There are two ways that we bill the credit card that is associated on the account. One is the Billing Cycle Day and then the Threshold Billing. I will briefly explain both and then explain how they work together. There is a one-time nonrefundable sign-up fee of $5 to your credit card. Then, we will charge the same credit card at minimum once per month on your billing cycle day, or every time that your campaign incurs $50 in advertising costs (this can be multiple times in a month period depending on the budget amount set), or reaches your billing threshold, whichever comes first. 

Billing cycle day (BCD): The day that you create an account will be your monthly billing date. Since the account was created an account on the 1st, your billing date will be the 1st of each month. This BCD can not be changed as it is the day that the account was created.  If the credit card has not been charged within a ten day period of the 1st, the system will charge the credit card for any balance owing.

*** this can be seen on the sub tab of Billing under Accounts & Billing Tab

Billing Thresholds: In addition to monthly billing, Microsoft adCenter periodically bills your account based on the amount charges that accrue. The amount at which adCenter bills your account is called the billing threshold. Over time, as you make timely payments, we will increase your billing threshold. The Threshold begins at 50.00 and after three successful payments within one calendar month, the account will move to the next amount and this will continue to grow.

***this can be seen under the sub tab of Billing within the accounts & Billing Tab

Budget Overview:

There are two ways to have the system use the monthly Budget that you set. Depending on your needs you can choose one of the following choices.

1. Divide the budget across the month

This budget option automatically adjusts your budget as the month continues. It predicts how many impressions should be served to meet your budget. Additionally, this option makes your campaigns less likely to go into a paused state.

*For an accurate division of your budget across the month, your ads might not be delivered for every search query. The ads are spread out across the month. 

2. Spend a budget until depleted

The campaign's monthly budget amount is spent as quickly as the activity demands. Select this option if you have a high budget or an unlimited budget. 

Hope This Helps !

 Elizabeth - MSFT