You need to also look at how you will keep the weight off when you get to where you want to be.
What is your plan for keeping the weight off once you get there? Do you plan on permanently eating less since your old way of eating and activity level clearly made you bigger than you would like to be?
As Kara mentioned - not exercising can result in you losing muscle when you lose weight. This has a direct bearing on how many calories you burn in the future. It is quite possible that after losing weight you could gain weight at a quicker rate than before if you return to your old lifestyle (since reduced muscle mass burns less of those calories leaving an even bigger surplus which goes to fat).
Many people that do not exercise come a little unstuck with this aspect and regain the lost weight.
For many of us - increased activity levels as a way of life is a major part of our long term plan for not putting the weight back on.