If you are cooking an average sized baked potato in the microwave, start with 4 minutes. Then turn the potato and cook for another 4 minutes. If your knife or fork slides in and out easily then it’s done. If not, try cooking for another minute on each side. If you are cooking your potatoes in the oven, it can about 20 minutes with your oven on 325 degrees. Check for doneness in the same manner.