BMR is just what it takes to keep your body functioning doesn't include activity. And I think that is really guess work and would say that is psuedo-science/medicine. more like a guideline. But a guideline I used as a jumping off point.

I am loosing 1-2.5 pounds a week from eating a range of 1100-1500. My BMR is roughly 2080 calories.

I also work out 3 times a week through weightlifting, then do softer exercise of tai chi/yoga 3 times. And I sit at a desk all day typing from doing software programming.

I read an article once about people who don't gain weight that easily and it said that those type of people burn the extra fuel off as heat off their bodies. Thought that was interesting.

For me it is a mystery, I would say something to do with eating the right types of foods in the necessary amounts. Only way to figure it out for your body is like Liz said trial and error.

For me it wasn't just caloric intake (cause I been on 800-1000 calorie a day diets, which left me hungry and feeling like crap. not loosing weight.) it was eating the right carb foods, lowering the carb intake and getting the caloric intake right with the other two.