How the billing anchor works

Every monthly plan on this store renews on the 2nd. That is a choice, not a limitation of the processor, and it exists so an account with four subscriptions has one renewal date rather than four.

The consequence is that your first period is almost never a whole month. It runs from the day you bought to the next 2nd, and you are charged for exactly those days.

A fixed-duration plan is outside all of this. It has no anchor because it has no renewal: the term runs from purchase and then ends.