Most Prisma employees never chose their contribution rate — the plan enrolled them at 3% and increases it 1% a year. That's a reasonable default, but Prisma's match is discretionary and wasn't funded in 2024, so there's no "contribute this much to get the full match" number to aim at. Here's how the 403(b) works, what it's allowed to do, and how to think about picking a rate yourself.