Everybody's bodies are different. You have to experiment by yourself as certain people have better metobilisms then other. Also, it doesn't have bodyfat percentage and a bodybuilder would be considered obese with this calculator.
It is similar to the answers that kendra and michael alias calculater that I started out with. I agree with Youngintricatemuscle I have used an equation that you put you lean body mass in to find out how many cals you burn. It gives you higher calories the more mass you have. And the activity level isn't exact though. It doesnt specify weight lifting 3-4 times a week as high or very high. Plus if you are busy like I am walking around at work and to classes it burns more cals. But either way it will give you a good starting point. If you want to gain weight start at 500-1000 cals above that. If you do not see the results you are looking for you can always add. The only real way you can find out how many calories you burn is too run a set amount for a week or two to see how your body reacts. I have used calculaters to determine how many cals to start out with, but since I have more muscle it requires more cals usually. So give it a shot, it is a good starting point at least.