How do you calculate push/fold on the bubble?

[Kandahar]

OK, I just got SitNGo Wizard to help improve my bubble play. On the "easy mode" quizzes, I average around 80-90% correct. But I really don't know what I'm calculating...I just go by whether it "looks right."

I know that some of you guys can just look at a hand and know whether to push or fold. Are you crunching numbers in your head, or just going off of experience? I'm pretty good at crunching numbers...but I don't really know WHAT I should be crunching.

Trying to estimate my current equity is hard enough, before I even consider fold equity, probability of winning a showdown, where my hand is on the Sklansky rankings, etc.

Does this just come with experience, or is there a mathematical shortcut that I can calculate in my head to decide push/fold?

[Kandahar]

Any thoughts?