At 236 pounds you could definitely lose 30 pounds in 2 months in a healthy way. In fact, I was 223 and did it, so I know that it's possible. But I wouldn't suggest that as making your goal. As mentioned, 2.5 pounds a week, or 10 pounds a month, is a good goal that you can achieve. So if you set your goal for 20 pounds, still try and do the best you can so that if you did lose 30 pounds, it's just an extra boost. When first starting you do lose more weight than 2 months into your weightloss so you may lose 30 pounds in 2 months. But don't expect it to be that way all the time. Like I mentioned, I lost 19 pounds in my first month. Then 13 the following month and 8 pounds the next. So it seemed to slowly decrease every month for me.