Your card will be charged for the first time on the official start date of your membership. Then, each month after that, your card will be charged on the same date. So for instance, if your official membership begins on July 4, you'll be charged on July 4, and the again on August 4, September 4, October 4, etc... Each of these dates is when your "service period" for the month begins.
You can find the date on which your card will be charged in your Billing History. To get there:
On your home page, navigate to your Profile page (either in the column on the left or the dropdown on the top right)
- On your Profile page, click Membership & Billing
- On this page, you'll see the Billing History section, with the Service Period column. This column displays a date range, and the first date of the row is the date your card will be billed on