This is a common question with no right or wrong answer. The best time to clean your windows is when you notice they are dirty. That usually is when you are seeing the sun come through or when you are at your sink looking out the kitchen window. Insides can be cleaned anytime of the year. For the outsides there are a couple of things to consider. The pollen can be a problem on outside windows. We have found the pollen is usually not as bad by the middle of June. Unfortunately it’s hard to wait that long to have clean windows! Many have their windows cleaned inside and out early Spring and then again late Spring or early Summer. Nothing like clean windows!