I'm 235 lbs w/23% body fat. my goal is 13% bf. can i expect to be at 13% w/20 lbs weight loss or too simplistic? i lift x 6 days a week run x 5

Too simplistic: As you lift and gain muscle, your weight is likely to rise (muscle weighs more than fat), so there is no way of predicting how much overall weight you need to lose in order to reduce your body fat. If you lost 20 lbs of fat, that would likely get you close to your goal. I would avoid trying to achieve particular numbers and instead rely on how you feel.

Too simplistic.: With weight loss, some will be fat and some will be lean muscle Your weight training along with a diet high in lean protein such as fish and whey protein supplements will minimize the amount of lean muscle catabolized as you lose weight. But I don't think the math will work out that easily.