If I eat 400-600 calories and burn about 800 calories per day..?!

Don't do this, this is eating at a starvation level, which is very bad for you and will make you sick and end up heavier than you started.

If your BMR is 1428, then that's the minimum calories your body needs to perform its basic functions. You are already burning far more than 800 calories a day, just in your vital organs.

If you eat only 400 calories a day, your body will go into emergency starvation mode. That means it will stop using fat like it was before and start consuming muscle, lean body tissues, and your vital organs like your heart, liver, kidneys and intestines will stop doing the things they need to do to make you a healthy person.

You may have lost a few pounds, but that doesn't mean you are getting healthier. If you continue doing what you are doing, you are setting yourself up for a lifetime of bad health.

Instead of starving yourself, you should be giving yourself about 1600 calories a day of good, healthy food like lean meat, vegetables and whole grains; avoid sugars and fast food; and get a moderate amount of exercise, walking or jogging each day.

You will lose a lot but you will either lose control and eat triple you normally do in a binge or you will put on double the amount you lost when you start eating normally again. And you Will need to eat properly again otherwise you will die. Best way to lose weight and KEEP IT OFF is to make sure you are eating at least 1200 calories. Even with this you will lose a lot quickly but it is also safe.

you are awful young to be worrying about your weight like this
and you are not eating anywhere near enough! try double the amount of calories you take daily, try things like pasta, it will give more slow release energy, remember you are still growing so you need a variety of foods to help you develop.
keep exercising its good for you ofc.
also some of the extra weight you have could be puppy fat, you could be due a growth spurt and when you do that extra weight you hate will spread out...thats what happened to me anyways

your too young to obsess over weight

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Well you burn on average 1,800 calories per day without doing anything so you will have to eat more than that. Also, burning 800 calories is not easy...I think you should stick to aerobics (treadmill and elliptical)