The length of time it takes to see results from a treadmill varies based on more than your exercise habits. You can eat away any weight loss benefits, treadmill or otherwise, with poor nutrition habits.  From my experience, if you successfully maintain (at least) a 200-calorie deficit per day while regularly using the treadmill for 45 minutes a day five days per week, beginners should start to feel a difference within a couple of weeks. You may start physically noticing a difference between two to four weeks. Other people will start noticing after you’ve stuck to it for about six to eight weeks.