Originally Posted by berkeleyguy3

500 milers are accrued based on "BIS" (Butt In Seat) miles -- what you fly on United operated flights. Every year, the ticker starts at 0, like EQMs. Unlike EQMs, you only earn BIS miles when you're flying on a United plane -- Star Alliance codeshares don't count. Each 10,000 BIS miles, you earn 4x 500 miler e-certs.

Hope that helps.