Calories for Consistent Weight Loss?

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when I started MFP, it set me at 1,200 calories per day. At the time, I was doing almost no exercising with it. I started to notice a trend of on the days I went over by 150 to 300 calories, I had lost more weight the next morning. I just reset my goal to 1400 but have not waited long enough yet to see if this is a good change for me. As of recent, I have begun exercising significantly more (running about 3/4 miles and walking around 1/4 along with weight training for approximately 45 minutes 4 to 5 days per week and Zumba 2 days per week) At this point, I'm not quite sure how much I need to be eating on a daily basis. As of right now, I am not eating back my exercise calories - really and truly, unless I start eating sweets and such, its impossible for me to eat my daily allowance as well as my exercise calories. Any suggestions on an appropriate calorie number?