If you pay over time for your membership, each month you will be billed on the exact date that you started your membership e.g. if you started August 17, you would be billed again September 17, etc.
If you have paid for your 12-month membership in full upfront, and you do not opt out of renewal, you will be billed again for another 12-month term on the exact date you began your membership 1 year later.