I was coming here to echo the 1-2 pounds a week being a healthy rate of weight loss. (2 pounds being a GOOD week, and does not happen every week!)
What I also wanted to add, is that the more overweight you are, the faster the weight comes off-AT FIRST. Meaning, someone who starts out at 160, trying to get to 140, will start out losing slow. Someone who starts at 250 trying to lose 100 pounds may indeed find that the first month the pounds come off faster-you might very well lose 4 pounds a week, give or take, in the first few weeks-as you lose though, the weight loss will start slowing down. This is normal!
You will not lose 4 pounds a week, or even 3 pounds a week, as you get closer to goal. (Unless you are completely starving yourself, and losing in an unhealthy manner.)
I am only letting you know this, so you don't set yourself up for disappointment with a goal that might be unreachable. You will lose the 100 pounds with a healthy diet and exercise if you set your mind to it-but it won't be 4 pounds a week.