Muscle gain and metabolism

How much does muscle gain REALLY affect metabolism? Let's say, for example, with the heavy weight lifting I've done all year, I have put on 5 pounds of muscle (a guess because it's hard to measure that without DEXA or something nearly equivalent). For a girl, I think that's supposed to be pretty good.

How much might this affect my BMR? Should I add 100 calories to my maintenance and weight-loss calorie goals? Should I ignore it? I haven't actually lost any weight on the scale (BOOOOOOO) but I can feel that the composition of my body is more muscular, especially across my back.

Ubntrained muscle burns about 5.7kcal/day per pound while trained muscle burns about 7.2kcal/day, so the effect of any one pound isn't very huge.

 The efffect of going from having 100lbs of untrained muscle to having 100lbs of trained muscle will however mean adding 150kcal/day to your BMR. So how much you need to add depends on what your current vs. old lean mass is - [(New lean mass*7.2kcal/day)-(Old lean mass*5.7kcal/day)] is roughly correct.

 And 5lbs of muscle in a year is pretty good for anyone dieting - Jay Cutler, with aboyt $20,000 dollars worth of drugs in his system and all the time in the world to train and eat right gains maybe 6-8lbs of muscle a year. Granted, he's far beyond his natural limit, but I think you're doing good :)

I'm guessing 5 pounds because I starting weight-lifting for the first time a year ago, and therefor went from having practically no back muscles to having decent lats and being able to do a pull-up, etc. If it's less than that, who knows. But I guess I'll just ignore it in the overall scheme of things. It's probably wise anyway not to consider having more muscle as an excuse to eat more (although it does confuse and frustrate me a little because I have more muscle than most skinny men, so why shouldn't my metabolism be as good as theirs?).

You'll probably like Melkor's answer better but what I have read agrees with his post that 1 lb muscle burns 7 cals. a day.  But in the article I read (sorry no link) it also said that 1 lb of fat burns 4 calories a day.  So if you gained 5 lbs. of muscle and still weight the same then you lost 5 lbs of fat.  This is good.  But the net calories difference is only 3 calories a lb. or for you 15 calories a day.  Not enough to warrant a change in diet.

On the other hand the scale will tell the ultimate truth if you start to lose then gradually up your intake, or of you start to gain, adjust your intake downward.

Hmm, isn't it about 2.5-3kcal/day for fat? Yeah, you're right though, still comes out mostly a wash as far as the 5lbs of muscle goes. However, don't underestimate the effect of increasing the calorie burn per pound of muscle - some very optimistic people have been fooled by that into thinking that each pound of muscle you gain burns an extra 50kcal/day by observing the net effect of gaining 2-3lbs of muscle by starting a new training program.

 That's attributing all of the observable metabolic increases only to the muscle you gained, which seems plausible until you stop and consider that in that case the muscle you already had remained unaffected by your training. This doesn't seem very likely ;)

 It's still not vastly significant, but you do probably burn in the rough neighborhood of 50-150kcal/day more, or 350-1050kcal/week. Well, in all likelyhood more towards the median value - it helps you go in the direction you want, but the effect isn't all that.