Weighing in day today, 4.5lbs loss this week and I won 'Slimmer of the Week' for the 3rd time! 
Didn't get the '1.5 Stone Award' this week as there is a 2.5lbs discrepancy between the SW scales and my home scales due to wearing clothing, and so I am half a pound off 1.5 stone loss at SW 
Home scales this morning = 16st 9.5lbs
SW Scales = 16st 12lbs
Start Weight = 18st 4.5lbs
Current Weight = 16st 9.5lbs
Target Weight = 12st 7lbs
Loss so far = 23lbs
As regards snacks, treats etc, I agree with all that @73kittycat73, @picklemewalnuts and others have said. For me, the ONLY method that works is to NOT have ANY snacks, treats or goodies in the house, that way there is no temptation. If there are treats in the house, I have no discipline, I WILL make allowances and excuses as to why I can eat bad food. It starts with the odd bag of crisps, biscuit, handful of peanuts, and it snowballs from there. In no time at all I end up back at square one. Food was my best friend, but now I have broken up with it and have some new friends, like my treadmill, tennis racket, spinbike...
As for BMI, I don't bother. There are just too many factors to take into account when measuring it, I very much doubt I would ever get an accurate reading. There is certainly no way Fitbit etc could possibly know my BMI, and any estimate is bound to be way out. So, I don't bother, I just stick to weight & inches, and they are both dropping.