If I am wanting to lose weight I calculate 25 calories per mile (6'2", 195#). This allows me to not feel like I can eat at 5 guys every night because I am riding every other day. I keep a food diary to see what inputs I am adding to the system. As others have said, most "gizmos" other than powermeters are fairly inaccurate. The online calculators are a flippin joke.
If I am maintaining I just watch the scale. Oh, and don't feel bad about asking anything on here, however as mentioned you may want to do a search as there is a TON of good reading to be done on this topic.