And why weight training? I'm trying to lose weight, not gain muscle.
I'll answer this first ... since it's more important. When you lose weight, you don't just lose fat, you lose fat AND lean muscle mass. In order to maximize fat loss, you want to minimize lean muscle. The only way to minimize lean muscle loss is to work the muscles and keep them strong and healthy.
The other reason you want to build/maintain muscle is that muscle is metabolically active. In other words, the more muscle you have, the more calories you burn just by "being" ... and therefore the more fat you'll burn throughout the course of the day.
So yes, you ARE trying to build/maintain muscle.
Where are you getting 1800 from? The calculator I used said 1600 but I figured why not do less than that.
I am getting 1800 from a fairly standard calculation as follows: The average moderately active adult needs 15 calories per pound of body weight to *maintain* their current weight.
For you that would be 170 * 15 = 2550 calories to stay the same weight.
Knock 30% off of that to get a healthy rate of loss.
For you that would be 2550 * 70% = 1785 calories to lose weight healthily.
Why not go lower? The idea here is NOT to drastically take everything as low as you can as fast as you can. The idea here is to have steady, sustainable, consistent weight loss, while keeping your metabolism as high as possible for as long as possible.
When you lower your calories, you lower your metabolism. When you lower your metabolism, then you have to lower your calories again to keep up. Then your metabolism lowers. Then it becomes a vicious cycle as you struggle to lower your calories enough to sustain weight loss. Whereas if you lower your calories JUST ENOUGH to lose weight steadily, then when your metabolism slows a bit and you lose that weight, you have wiggle room to lower them some more, as opposed to just hitting rock bottom right out of the starting gate, and having nowhere lower to go when you stall out.
Make sense?