Eating for weight you want to be?

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I'm 132lbs at minute and my BMR is 1,239. MFP has me on 1,200 cals a day so have 390 cals left for dinner.

(I just had 2 slim fasts, 1 breakfast, 1 lunch - an apple and 2 ryvita with a spread on thinking they were healthiest low cal options and they come to 810cals already! )

I'd like to be 126lb (9st) so wondering of this eat for weight you want to be would work as i seem to stuck on 1,200 that MFP has set me.

For 126lbs my BMR would be 1,212 so that's how many calories I would have a day instead of 1,200? that gives me 402 cals left instead for dinner. I'm not sure if I'm meant to calculate TDEE in for this 'eat for weight you want to be'? I usually go with sedentary then if I do manage a bigger workout I have an extra treat if I'm gonna end up with too big a deficit.