Your billing schedule anchors to the day you signed up.
Example (7-day trial): sign-up on January 5 >> trial ends January 12 >> renewals on February 12, March 12, April 12…
If you signed up on the 29th, 30th, or 31st, your renewal falls on the last day of any month that's too short to have that date – for example, a January 31 sign-up renews on February 28 (February 29 in a leap year), then back to the 31st in March.
Your exact next billing date is always shown in your account settings, and every charge comes with an email receipt showing the amount and your next date.
To avoid the next charge, cancel before your renewal date – see Canceling your subscription. Plan prices are listed in Plans, pricing, and renewal.