Calculating a "breakeven point"??

maybe explain a bit further what you mean

do you mean maintenance cals?

BMR is the basal metabolic rate, or the amount of calories your body uses just to maintain itself when you do nothing but sleep 24/7. RMR is the resting metabolic rate, which is the amount of calories the body burns while resting and it is slightly higher then the BMR. Some people use the term RMR for the Daily Activity not counting exercise because they are "resting" from exercise. A "break even" point would be the total amount of calories burned so that if you consumed that amount of calories you would theoretically maintain weight. That would be the Total Daily Energy Expenditure which is BMR + Daily Activity + Exercise. A simple way to estimate it would be 1 calorie per kilogram per hour for the BMR, then multiply by an activity factor and add in exercise calories. The activity factors are 1.2 for sedentary (adds 20% to the BMR), 1.3 for lightly active (adds 30% to the BMR), 1.5 for moderately active (adds 50% to the BMR), 1.7 for highly active (adds 70% to the BMR), and 1.8 for extremely active or athlete (adds 80% to the BMR). So, here's an example of how to figure TDEE:

100 kilogram (220 pound person); moderately active; burns 300 calories in their daily workout

100 kilograms x 1 calorie x 24 hours = 2400 calories for BMR

2400 x 1.5 for moderately active = 3600 calories for RMR or Activity Calories

3600 calories + 300 exercise calories = 3900 calories for the TDEE

Then use the TDEE to subtract from for the loss. I use a modification of this formula using the lean body mass instead of the total body mass for my clients and no more then 20% subtraction for weight loss.

The difference between this and what MFP does is that they have their own proprietary formulas and they don't add the exercise calories before subtracting out for losses and they use 500 calories per day for 1 pound a week loss and 1000 calories per day for 2 pounds a week loss instead of the 20% rule. Because they've already done the subtraction not counting exercise, that is why you can eat your exercise calories back.

EasyPeasy:
http://www.migrelief.com/calculate-the-calories-you-need-for-maximum-weight-loss-results