How significant will my weight loss/weight maintain be?

If i cut out all junk food from my diet and eat healthy, calorie counting, switch to whole wheat, etc.. with the exception of one cheat day a week (so i dont go insane) and take my dog for at least a 30 minute walk day, will i lose about 10 pounds and then maintain my weight. I HATE the gym. I will also be taking little excersise steps such as parking in the back of the lot. I am 19, 5'4 and 125 lbs.