The formulas used in the Healthy Body Calculator® are proprietary but I can tell you that they are based on published research and current nutrition practice. Your current body weight is 1 factor that determines calorie needs. The more a person weighs, the more calories they need to maintain that weight. So it is possible that even on 2150 calories per day, you may lose weight.
The only subjective data you enter into my Healthy Body Calculator® is your activities. Did you overestimate your activity? Do my calculator again and don’t put in any activity hours. That calorie level result would be your BMR (basal metabolic rate) which is the number of calories you need just to keep your body running while lying awake in bed. This is assuming you did not choose to lose 1 to 2-pounds a week in the calculator. So when you get up and do whatever you do during a typical day is your activity calories which would be added to your BMR. Re-do the calculator again and now add in your activities, not exercise. What is the difference in the calories you need to keep your body running (BMR) and how many more calories do you need for your activities?
Bottom line starts with the Calorie Goal in Your Nutrition Facts with your activity hours included. If after 2 weeks, you have gained more than 3 pounds, then you would need to lower your calorie intake by no more than 500 calories. Definitely, don’t eat less than 1200 calories per day as you won’t reach your Recommended Dietary Allowance for vitamins and minerals and may experience hunger which could trigger binges.
You see, if you try to eat a very low-calorie diet (VLCD), skip regular meals, you may increase your bulimic behaviors. You need to eat a moderate amount of food in 3 meals each day and eat every 4 to 6 hours even if you aren’t hungry. If you wait until you are hungry, you may binge on whatever food is handy.
BTW your BMI (body mass index) is an estimate of your health risk, not body fat.
I do understand your fear of gaining weight. Isn’t that why you started bulimic behaviors? You don’t want it to control your life anymore. Congrats for dealing with a very difficult health issue.
Perhaps now is not the time to stress yourself further with a weight loss goal. Would it be acceptable for you to just maintain your weight until you get your bulimia under control? That would be a reasonable, healthy goal. It is difficult to change more than 1 lifestyle behavior at a time. Then once your bulimia is under your control, set a moderate 1 to 2-pound weight loss goal. You can do it!