How much exercise do you have to do to burn off 500kcals?

The activity and the amount of effort will change the rate of energy expenditure. For male at 20 years and weighing 180 lbs or so, an hour of swimming will cost you 800 C, an hour of cycling 500 C and an hour of running 771 C, There are also considerations for your age, sex and weight. It is better to find a calorie calculator on line and insert your specific data rather than use a "one size sits all" answer.