How do ratings work?

[DirtySixThirty91]

So someone please explain to me how the rating system works. I have a mostly 99 team and play another team just like mine who has a much higher rating than mine and I win. I get like +15 to +20 on avg.

But the other day I lost to a team who was 145- 38 and almost 150 more in raitings I get destroyed and I lose -34 points on my raiting.