900 calorie defecit?

I'm 16, I weigh 173. I was wondering if a diet of 1,250 calories a day with a 900 calorie defecit was healthy. Too low? Too high? I don't want to go into starvation mode, but I'd like to lose weight at a reasonably quick rate.

You're in the "safe" range for an adult, though in the lower range for calories in/higher for deficit, but I would suggest looking further into this on a teen/kid site.

You're still a growing girl.  What was your BMR?  I would recommend exercising as much as you can and still eating and getting in those calories.  Just make sure they're healthy options.  Besides, the faster you lose it, the faster you are likely to put it back on if you don't keep in line with whatever method you used to lose it.

Hi  try not to put your body into starvation mode.

Yeah, I'm trying to be careful not to do that :]
I've been trying to get in as much activity and exercise during the day as possible, it's just the calorie intake that has me worried. If I eat over 1,250 I feel like I'm binging..

You are eating only 1250, then burning about 2100? Is this correct? If so, you are not eating enough. I would try upping it to 1500-1600 and adding higher calorie healthy snacks to prevent feeling overly full, but still get you cals in. It's okay to go a little lower, but I wouldn't aim for 1250. Besides, you are young and your body needs more.