This seems to be a fairly accurate calories burned/power calculator. This is a good way to figure out your daily calorie burn and estimate calorie intake goals for weight loss.

Measure your resting heart rate for one minute. Use that as your average heart rate. Use that heart rate for 23 hours per day=1380 minutes. Then if you plan to exercise for one hour per day at the gym, use your average heart rate 110-150 bpm at the gym for 60 minutes.   Add the total calories burned together and that is your bodie’s daily calorie usage. Eat less calories than that and you will lose weight.