BMR/RMR Defined
What are these numbers? Before you can establish your daily calories let's understand what these two terms mean. BMR is your Basal Metabolic Rate and RMR is your Resting Metabolic Rate. Honestly, these terms are interchangeable as the calorie difference and what they are so small that it doesn't factor into your fat loss. You will see all over the internet people talking about both but they mean either term.
BMR/RMR is simply the amount of calories you burn in a day to live if you stayed in bed and did nothing but breathe and sleep. This DOES NOT include calories from exercise or general life like driving your car, cooking dinner, washing clothes, walking to the boss' office, etc. Through the day you burn more calories than the base BMR/RMR number.
Many BMR/RMR calculators give you an activity option. This means they are going to generically factor in how active you are on a weekly basis and give you a new number to maintain your current weight that includes your typical lifestyle. (In the above post that's where we multiply by 1.2 - that's the lifestyle factor of lightly active).
Finding Your Target Calories
For our purposes, let's play with the following calculator since it factors in the lifestyle number for you in an easy way.
http://walking.about.com/cs/calories/l/blcalcalc.htm
Lightly Active would be those who exercise 4 days or less, walkers who don't strength train, or cardio only type people. Yes, if you aren't strength training you go into light activity because you are killing off your muscle tissue which makes you burn less calories from your muscle pumping couterparts. You burn anywhere from 800-1200 calories a week (using your HRM).
Moderately Active would be most of us. You exercise 4-5 times a week, doing interval workouts, burning around 300-400 calories per workouts, and strength train once or twice a week. You burn anywhere from 1200-2400 calories per week.
Very Active is for people who are serious about the lifestyle. You exercise six times a week, high intensity cardio is your BFF, and you are lifting like a real woman three times a week. You probably sneak in bonus activity, too, by doing active things on the weekend that's not exercise but you are still scorching some calories. You are burning at least 2400-3600 calories per week.
Extremely Active is for athletes and Jen who teaches several fitness classes a week on top of her own grueling schedule. :) Just had to give her shout out. Most people in this category rack up around 4000+ calories burned per week but only use this category if you are a conditioned athlete. Some heavier, deconditioned people will fall into this category for a few months until their body catches up to their new lifestyle.
Now, you will take the number given to you in the calculator and subtract 500-750 calories to acheive your daily calories you should aim for each day of the week (never dropping below 1200). For Weight Watcher girls, take that number and divide by 50 or 60 (if you eat lots of fresh and high fiber foods - no junk) to get your points.
The key to losing weight is to keep your body just barely underfed to meet the demands you are placing on it. Undereating and overeating are the same in my book. Both will store fat, both will make you feel terrible, and both are unhealthy.