Hello and good day,
Does anyone know how flight distance is calculated?

Just adds it up, I think. More or less.

Hi. Thank you for reaching out to DJI Forum. With regards to this query. I will forward this inquiry to our designated DJI support team for further clarification. Once we have the information needed we will be sending you a notification. Thank you for your patience and support.

Hi. Thank you for creating this post. As advised by Glenn Goodlett at post #2. It will be the sum of all the flight missions of all your DJI drones flown on your DJI account. If you have further concern or inquiry, please feel free to post it here at DJI Forum, we are here to help. Thank you.