At 20% BF, if you are lifting and doing cardio 5-6 days/wk, the rule of thumb multiplier is 12-13 calories/lb of body weight to cut. At 20% BF, you're probably not that much above maintenance levels at this point. Figure out what you're eating (say 2500 calories/day) and start to cut back by 200 each week (2500 to 2300 to 2100, etc) until you reach your range. Stay there. Macros for cutting - if you're not carb sensitive, you can go as high as 50C, 30P, 20F using clean carbs and essential fatty acids for your fats. Other good ratios are 40c/30p/30f or 40c/40p/20f. The stickies on the top of the women's bodybuilding forum are excellent for diet - we seem to be really fixated on food!