Calculating homemade yogurt's fat I'm currently using a very "rich" whole milk with 3.8% fat. Out of one liter milk, I get 850cc yogurt (as some part of the water will evaporate throughout cooking. 
The question is: how much fat will contain the yogurt?
A stupid calculation would be

3,8% divided by 1000cc = 0,38
3,8% divided by  850cc = 0,44


Is the math correct? Is this yogurt extremely fat?
This is the correct calculation. There is nothing going on in the yogurt to change its fat content. (You can't use a similarly easy calculation for carbohydrates, as the culture consumes some of them). 

Your math is correct. Is it "extremely fat"? In yogurt-terms, not at all. I have regularly seen 10% yogurt from cow's milk; yogurts from other species can easily be fatter. So, compared to general yogurt numbers, it's just a normal yogurt.