Personally, I believe "goal by" dates are generally a bad idea. If at any point you lag behind your goal schedule, you can become tempted to do unhealthy things to "catch up." Also, your weight is not under your direct control. If you stick to your food and exercise plan perfectly, you can't guarantee that your weight will be x, y, or z.
Instead, I would suggest a goal that you have complete control over. Sticking to your food plan, exercising x minutes, y times per week, drinking z ounces of water daily.... In other words, rewared "actions" not "results," because "results" happen on their own.