Fitday will help you keep track of you're macros, but not help you determine the ratios you need. When cutting, the general ratios are either 40/40/20 or 40/30/30 (P/C/F). However, you may need to tweak these ratios for you. Some people are more carb sensitive than others. Those ratios are a good starting point. Monitor your progress and adjust them as needed. You DO need fat in your diet and your fats should be equally divided with saturated, polyunsaturated and monounsaturated. EFA's are essential as well. Also regardless of your carb intake, make sure you get enough fiborous veggies.