Your weight is matching your deficit. If you're not losing, there is no deficit. If your not losing as much as you expect, it's because your deficit isn't as big as you think it is.
Unfortunately, there is no practical way to measure your actual calorie deficit, and to make it worse, dieting itself, can reduce the number of calories your body burns (both at rest and in activity). So if you cut 500 calories per day, and your body in response (trying to conserve it's energy) burns 250 calories fewer - you'll expect twice the loss that you'll actually get, but cause you have no way of knowing that you're burning fewer calories than before you started cutting calories.
A recent study (about a year ago, I think) comparing actual weight loss results with the weight loss predicted by the standard calculators (which treat metabolic rate as constant) found that (on average) weight loss results end up generally being about half of what the "math" predicted.
So if you're completely average, you can reasonably expect to lose only about half what the normal math tells you to expect (which means the math we're all used to using is wrong).
It turns out calories aren't all equal. Eating more whole foods (especially high fiber foods like fruits and veggies, raw especially) can help increase calorie deficit, because your body has to burn more calories to digest them than more easily digested foods.
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