Calories burned, is it all voodoo? hr monitor, elliptical, and online calculators differ by up to 50%. is one more accurate? i'm 250 lbs, ffm 180 lbs

Overestimate: I do believe MANY machines in gyms and online calculators grossly overestimate calories burned. Probably a high quality programmable hear rate monitor is the most accurate.

Extremely dynamic: For weight loss, you should have net cal deficit. With exercise it can be difficult to monitor the exact Cal burned. Reason is mainly because it depends on your basal metabolic rate and how effectively the body can release the CO2 from lungs. Don't try and count every Cal because it is extremely difficult. Instead, aim for cutting portions in half and performing various activities almost daily.

Depends on input: Any device that estimates calories burned using more of your body's own personal information or your actual mets of work performed will be more accurate. For example, a ellipticalmachine which uses your weight and measures the work performed will be more accurate than a table of how many calories are burned doing an activity for a half hour. Your heart rate measures fitness more than calories.

Beware the machines: While exercise machines attempt to alert users of calories burned and wattage acheived, the reality is unless in a sport medicine clinic, you probably are not getting accurate results. I am a strong proponent of regular exercise, and then increasing intensity and duration as tolerated. However, it is what you put in your body that is going to make the biggest difference to your fitness goals.

Calories burned: It is not voodoo, but there are many factors involved in making an accurate determination and most machines can only do a rough estimate. To do an accurate determination of exactly how many calories you burn during exercise, you would need to be in an exercise physiology lab where exact measurements could be obtained. Not likely in the local gym. Use the numbers as an estimate.