This is something very special about PHLAT membership: Members can choose (and change) their own level of membership by themselves (anytime).

How does that work?

It’s very simple: To become a member, a donation is required. The donation amount is the annual level of membership. Additional donations of the same amount result in (one-year) extensions of the membership. If a member wants to increase or decrease their level of membership, they can simply donate a different amount — the new amount becomes the new annual rate, and any unused portion of the current membership will be recalculated according to the new membership level.

These calculations are always documented in the confirmation email.