For
Nancy and the folks who did want to do a little math for weight loss . . .

It goes with the review of the basics idea this week but I'll skip the QOTD portion.
There isn't much new to say in this area -- weight loss is going to happen when you burn more calories that you take in. It takes 3500 calories to lose a pound. If you end up with a calorie deficit of 500 calories a day you will lose 1 pound a week. Sure some things may affect that from week to week but the basic premise doesn't change.
But how do you know what those numbers are?
First, you calculate your basal metabolic rate, also known as your BMR.
This is the rate of calories that you would burn if you were lying in bed doing nothing.
If you've noticed that every year, it becomes harder to eat whatever you want and stay slim, you've also learnt that your BMR decreases as you age. Likewise, depriving yourself of food in hopes of losing weight also decreases your BMR, a foil to your intentions. However, a regular routine of cardiovascular exercise can increase your BMR, improving your health and fitness when your body's ability to burn energy gradually slows down.
This calculator will help you figure out your BMR
http://www.bmi-calculator.net/bmr-calculator/
Once you know your BMR then you plug that number into the Harris Benedict Equation.
The Harris Benedict Equation is a formula that uses your BMR and then applies an activity factor to determine your total daily energy expenditure (calories). The only factor omitted by the Harris Benedict Equation is lean body mass. Remember, leaner bodies need more calories than less leaner ones. Therefore, this equation will be very accurate in all but the very muscular (will under-estimate calorie needs) and the very fat (will over-estimate calorie needs).
To determine your total daily calorie needs, multiply your BMR by the appropriate activity factor, as follows:
If you are sedentary (little or no exercise) : Calorie-Calculation = BMR x 1.2
If you are lightly active (light exercise/sports 1-3 days/week) : Calorie-Calculation = BMR x 1.375
If you are moderatetely active (moderate exercise/sports 3-5 days/week) : Calorie-Calculation = BMR x 1.55
If you are very active (hard exercise/sports 6-7 days a week) : Calorie-Calculation = BMR x 1.725
If you are extra active (very hard exercise/sports & physical job or 2x training) : Calorie-Calculation = BMR x 1.9
Total Calorie Needs Example
If you are sedentary, multiply your BMR (1745) by 1.2 = 2094. This is the total number of calories you need in order to maintain your current weight.
http://www.bmi-calculator.net/bmr-calculator/harris-benedict-equation/
Both of those calculators come from a site called bmi-calculator.net