OP - As others have stated, there isn't any algorithm. Upgrades are based on rolling EQD and impacted significantly by routing / timing. So far this year I'm 8/9 on eligible flights with about $27k Rolling EQD. The more you spend, the more likely of an upgrade. I've certainly been happy with my upgrade rate so far this year. I think I was probably more in the 60-75% range last year but I have some flexibility in my flight times. Hub to hub is always harder especially in peak times. The one miss I had was yesterday late afternoon PHL-PHX. I was
#4 on the list and I don't believe anyone was upgraded. My one highlight this year was scoring an upgrade on PHX to CLT which was on a 330 with lie flats. Nice surprise. That was a gate upgrade that I was
#1 on the list (I think 2 upgraded). This is also with a 28 seat F cabin.