How are Jackpot Challenge winners selected?

The draw runs once a month, early on the 1st (US Eastern time). Each pledged point is one entry, and winners are picked at random, weighted by entries, so more entries mean better odds. Each person can win at most one prize per draw, and recent monthly winners sit out for 60 days.

You can see how many entries you have for the next draw on the Jackpot page ("You have N entries") and in the dashboard header.