The graph below shows my recommendations regarding total screen time, depending on your age and the device that you use. If your 12-year old child uses a desktop computer only, she can spend up to 2hr per day on it, provided that you ban all other screens (TV, etc.). If your only computer is a laptop, the daily limit is 40min (i.e. 3 times less). If you use a smartphone only, the limit is 20min (i.e 6 times less).