Training for a triathalon and cannot figure out calorie expenditure

So i am starting a 12 week training program to do my second triathalon. I have been maintaining the 50 lbs weight loss i already had for the last 6 months, but now really want to lose the final 20 lbs.  The problem is that in this 12 week program, the amount of exercise i am doing is changing substantially from week to week (1st week is 200 min, 7th is 500 min, week before back down to 200).  So how do i determine my calorie intake (my active metabolic rate-500 to 1000 calories) if i am changing my exercise expenditure from week to week.  Should i determine it for each week? Its really confusing, but i know im going to have to up my calories during the process ti avoid going into starvation mode, and then decrease them as i taper off my workouts closer to the race. 

 Its like a math nightmare.

wehn I was training for my tri last summer, i would stick to my base cals of 1500 cals a day. wehn I worked out, I would up my calories as needed. but it was day by day depending on how hard i was working out. i added teh activities in teh activity browser and just made sure i only had about a 1000 cal deficit. just make sure obviously that you are getting enough cals to keep yourself goign through all the training. good luck!

I did the same thing that Ktcort13 did... figure how many extra calories you burned in exercise for each workout and factor that into you calorie intake for the day.  I wish you success.  Keep up the great work!