The tool applies the UK average life span of approximately 80 years for the lifetime calculations. If you are using this tool and over 80 then it applies a 10 year time frame.

On an iPhone simply load up the Screen time application on your phone. It needs to be enabled to start tracking your use.

On an Android device go to the settings and select the Digital Wellbeing & Parental Controls.

The tool uses a time period of 18 hours for each day. This is to factor in an average sleeping time of 6 hours per day.