For a full year while I was at home, I used the actual software and I could customize the "LIFESTYLE" on there. When I would open it up it would show how it calculates (such as getting 8 hours sleep). I would adjust it to what I actually did in day (such as less sleep, but time doing other things); just to be more accurate. Can you do that with the on-line version?
It looks to me like the activities are just like food. You tally your activities and fitday keeps track of them just like it keeps track of food - and you can produce reports from that.
I think it calculates your resting activity based on your weight and how active you are. Everything above that is added on. Then you can actually see from a report whether you burned more than you took in, energy-wise, each day.
I've never used the software but the online stuff works fine for me.