Does doing the same Exercise everyday decrease the amount of Calories it burns?

I have been running for about 2 weeks now, and using a App on my iPhone to keep track of everything I eat and doing. Today, I have noticed that, I put in about the same amount of time I ran and the about the same speed and distance, but it show I have burnt like 30 calories less. Why is that?

If Your Intensity Is Not As High Or You Lost Weight Then Yes Your Calories Burned Will Go Down

Samuel is correct, however you also have to remember that if you are doing the same general workout, your body will become accustomed to that workout. So if you want to work more calories off, and increase your ability to run more, try doing wind sprints at about 200m. I would recommend doing the same amount of running you have been doing, but break it up into sprints, with 60 seconds of walking in between them. This will change the way your muscles need to work, it will give make your fast twitch fibers spark and induce major calorie burn. Also change your running routine regularly, if you ran 30 minutes all this week, try for 40 next week, or start the workout with 10 minutes of jogging, then 5- 30 second sprints. This will shake your body loose.