I've learned to avoid setting any goal by dates. For me, they're just too damaging in the long run, because if I set a 20 lbs goal and lose only 15 by the deadline (or even 19.5) I always felt like at least a partial failure. Also, if I got behind schedule, it became very tempting to try to "catch up" by using very unhealthy methods. Making weight loss any kind of race with myself was just a horrible idea.
If you can do it without those pitfalls, and if you can reevaluate your goals if they turn out to be unreasonable, then shoot for it if you must, but realize that there's no way we can tell you if your goal is realistic or even possible. When I was in my 20's at my current weight, I could easily lose 8 lbs a week or even more, and now with insulin resistance and other health problems, my weight loss can be very unpredictable, even when I'm "doing everything right."
Personally, I think goals should be based on things you can control directly, and weight isn't that. You can only precisely control how much weight you take off, if you're using a chainsaw (don't recommend it, very messy). Losing weight isn't a direct action, it's the result of direct actions, so setting your goal based on direct actions makes more sense. Things like "I will exercise 1 hour, three times a week," or "I will use a food journal and follow my food plan."
In other words, make "rules" for yourself and follow those rules the best that you can, whatever weight you lose is your reward. If you aren't losing weight, then you need to change the rules, but you won't feel like you've failed if you don't see the rewards you were hoping to.
Last edited by kaplods; 02-27-2009 at 11:17 AM.