calculating exercise and calories

I have recently started a 1200 cal per day diet and I bike 40k or 2 hours  3 times per week.

according to my computer on my bike I use up approx 500 calories in this time frame, but on line on different sites it calculates to over that for half the time.  In otherwords they say I use up approx 1300 in 120 min for my weight and speed on the bike.  

My diet calorie calculator on line adds the calories burned in my bikeride to the calories for the day.  this would mean if I go by what they say on line that I need to have 1300 more calories on those days!  does this make sense? That is a lot of calories, over doubles my daily calories.  will I loose weight that way?