Fitbit Steps

It depends on your personal stats (gender, age, height, weight, BMR); weekly weight gain/maintain/loss rate; and what MFP Activity Level you chose: Sedentary, Lightly Active, Active, or Very Active.

The Fitbit reports your total daily burn to MFP; MFP provides the Fitbit Calorie adjustment based on how many more Calories Fitbit reports when compared to your MFP Activity Level goal.

I am male, 56, 5'8", 150 lbs., set to MFP Active in maintenance. I start getting positive Fitbit Calorie adjustments at about 5500 steps.

I would recommend reading through the first three posts in this thread on the MFP Fitbit Users group...

http://community.myfitnesspal.com/en/discussion/10098937/faq-syncing-logging-food-exercise-calorie-adjustments-activity-levels-accuracy

http://community.myfitnesspal.com/en/group/1290-fitbit-users