I agree with everyone else. Weight loss depends on your food intake. If you want to do it right, IMO, don't even factor exercise into your weight loss. That doesn't mean don't exercise, because exercise is important whether you're trying to lose weight or not. But focus on your food for weight loss and focus on riding to maintain your health. Plus this, also IMO, prevents the tendency to want to eat back calories you burned. Focus on a 2,000 calorie a day diet, and any calories burned through exercise is just an added benefit.
But as far as how many calories you can burn by riding your bike, well, that all depends on you. It depends on how much time you have to ride, how hard you're willing to push yourself, etc.