There is lots of advice out there on how to cut calories. We've found one of the clearest and widely agreed-to sources of information is from the Centers for Disease Control (CDC), the official health organization of the United States. Start with their article on Cutting Calories.

Starting an exercise program is simpler, but there are still some useful guidelines. Try the CDC's Physical Activity for a Healthy Weight.

How the Weight Loss Calculator Works

The Science Behind Calculating Weight Loss

While losing weight involves many variables that change from person to person, there is still a core science that can be the basis behind planning a weight loss strategy. The widely-accepted science behind the weight loss calculator is:

• One pound of mostly-fat body weight is the equivalent of 3,500 calories of either food or exercise.
• The appropriate amount of calories to cut from your diet is between 20% and 40% of your normal calorie requirement. See the CDC.
• Moderate exercise is considered to be 4.5 METs. (A MET is a rate of energy expenditure, similar to watts.) Vigorous exercise is 7 METs. Calorie consumption is: 1 calorie (technically, kilocalorie) per kilogram body weight per hour per MET.

Limitations of Body Weight Color Coding

The math behind the body weight color coding, something called Body Mass Index (BMI), is applicable and useful for about 95% of the population. It is not useful for highly fit people (who won't be using this calculator anyway). It is also not useful for very tall people. Use the color coding as a guideline for evaluating your body weight. Don't use it as a medical diagnosis.

Calorie Reduction Recommendation

This is a reduction compared to your estimated nominal calorie consumption, meaning the amount of calories you consume while staying the same weight. If you are currently gaining weight, you need to reduce your calories even further.

Keeping track of how many calories you consume is not easy. WebMD has a good food calorie list.

Examples of Moderate Intensity Exercise

• Walking briskly (around 3 miles per hour)
• Water aerobics
• Bicycling 6 to 10 miles per hour
• Tennis (doubles)
• Ballroom dancing
• General gardening

Examples of Vigorous Intensity Exercise

• Jogging or running
• Hiking uphill or with a heavy backpack
• Jumping rope
• Tennis (singles)
• Aerobic dancing
• Heavy gardening (continuous digging or hoeing)
• Bicycling 10 miles per hour or faster
• Non-casual swimming laps