That answer is that it doesn't quite work like that. Basically, any Star Membership payment simply pushes your Star Membership expiration date back by one year from your most recent payment. So if you make a purchase today, your new Star Membership expiration date will be February 13, 2027.
The recurring subscription memberships work like that too -- when people set up a recurring monthly payment, essentially they get a one year Star Membership each time, but they just push their expiration date back each month. If they stop making monthly payments, they still get a year of Star Membership from the time of their last payment.
Before we had ads on DU (more than 20 years ago), payments were simply donations, but after we started running ads and we introduced the Star Membership concept, where you get to hide ads, and receive various other things for your payment (like hearts to give out), they're now considered a purchase. But when we switched over from the original system, there were a few issues to overcome. People were used to making donations multiple times a year -- and we appreciate that, because it helps fund the site -- so we had to come up with a way that would let them do that, while also technically making a purchase, and that, combined with the "pay what you want" approach, combined with the limitations of PayPal's automatic payment system, meant that we ended up with the "push your expiration date back" system that we have now.
I was going to say I hope that makes sense, but to be honest, it probably doesn't. It's just the way we've done things for the last 20+ years 
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