BMR on dashboard but no Fitbit device

[Christakimoooo]

Hey all, I'm new to using the Fitbit app and something confused me. I saw my calorie burned total increasing as I was sitting at work. After a bit of research, I found out that this is due to my BMR. My question is, how can the fitbit app calculate my BMR when I do not have a fitbit device? It it using my Apple Watch? Or is it simply using my data such as height, weight, activity level, etc.? 

Thanks in advance!

[WendyB]

Its just using your height, weight etc

The calories burned are BMR calories. Your fitbit also calculates calories burned for your BMR. You burn calories just by being alive! Even Sleeping. Fitbit includes these burned calories in it's calorie calculations, so even if you did not wear the fitbit, you'll still burn these calories.

Read this

http://help.fitbit.com/articles/en_US/Help_article/How-does-Fitbit-know-how-many-calories-I-ve-burne...