Help with TDEE/BMR and calories

I'm currently 204, 5'7, age 27 and do 20 minutes of circuit training (30 DS) 3 days a week and cardio 4 days a week which presently includes couch to 5K (beginner levels) so 8 minutes of running and 20 minutes of fast pace walking at 1% incline and then I continue walking at various paces for an hour to 1.5 hours afterwards. I did the BMR and TDEE calculations based on moderate exercise and the results were.

BMR: 1724
TDEE:2672
TDEE-15%=2137

I've been netting an average of 1200-1300 so far and realize that is too low? I've changed my MFP calorie goal to 2137 is this correct? Should I be eating this many calories even on days where my only workout is the 20 minute circuit or on occasional days off? Do I need to recalculate my TDEE and BMR every time I lose a bit of weight? Does the calculations look right?