Axisandallies.org has a pretty good calculator - look on the ribbon of home/help/search/profile/my messages/members/AACALC/logout
I’ve heard some people don’t have this on their ribbon for some reason.
Oh, Zhukov gave you the direct link to it.
You do have to modify it a little for G40. If there are 2 AA guns and >5 planes flying over, I just subtract a fighter and don’t check the AA gun box. I enter AA guns as bombers (along with converting that number of infantry to “bombers”) to approximate. Be sure to change the order of loss to put “bombers” first, and delete the other “bom” entry in the defensive OOL.
You’ll have to approximate for things like tactical bombers too, of course. But the site’s calculator gives you a complete distribution of results as well as highlighting means, medians, and 1 or 2 standard deviations above or below.
I use another, older, calculator that is quirky but has some unique features and also gives a complete probability distribution. I want to know what the chance is that I start losing aircraft to take a territory, for example. Triple A calc is quite limited by not giving you distributions. Don’t ask for it - even getting it set up and working is quirky. Between these two calculators (the one on the site is sufficient, I think) I have a very clear idea of what I’m getting into and what the chances are.