Let go of that number. I know that a lot of trainers and coaches believe in the number on the scale as a means of motivating a client toward a goal, and to keep them moving, but I've never really had a client's motivation drop by convincing them to find their best body regardless of the numbers involved. Yes, if you are very overweight, and you do everything right to lose all excess body fat, the number on the scale will go down. The number on the measuring tape will go down as you lose inches (a sign of strong, tight muscles and a loss of body fat). But, this does not need to be your number one focus.
I have clients weigh in every few days, or once a week, if they so choose. Our weight fluctuates throughout the day based upon meals and water retention. Weekly, you want to be headed in the right direction. That is what matters.
But here's the real math: Prioritize adopting a lifestyle that will bring you to your best shape and level of fitness permanently. Once you get there, you will know what number is best for you. If you decide upon 120lbs., and you reach 127 but feel AMAZING and better than ever, happy and fit, that might be your new number. Be flexible. Listen to your body. Choosing a number out of thin air is presumptuous and sometimes dangerous in terms of discouragement (a deterrent to a healthy lifestyle). Eat well and exercise properly for LIFE and you will inevitably find yourself in your very best possible shape, and will be excited about whatever numbers sits on the tape or scale. And those jeans will make your butt look unreal (sidenote). ;)
*featured image found at www.ingoodfeather.com *internal image found at www.thatsfit.ca