Charge 2 shows calories upon waking up even when I didn't wear it to sleep

[Nicwills]

Put my fitbit on this morning and it said I has burned 456 calories! I dont sleep wearing it so where have these calories come from? I'm using the food log for a caloric deficit

Moderator Edit: Clarified subject

[SteveH · Accepted solution]

As well as tracking calories burned through activity your fitbit also tracks your BMR calories. These are the calories you burn just keeping your body alive (even when asleep). They are calculated from your profile settings for age, height, weight etc so you needn't be wearing your fitbit to get them. What you are seeing includes the total BMR calories burned since midnight

[wtksk8r]

Fitbit tracks/estimates all your calories, including those that your body burns to stay alive. This is called the Base Metabolic Rate or BMR. It is based on your stats - gender, age, height, weight... You can check the accuracy of the estimate by going online and looking for BMR calculators. 

[Nicwills]

So basically,  its guessing how many calories I've burnt whilst sleeping? I'll have to experiment now! Sleepnwearing it and see how it differs. Thank you so much for this reply

[SteveH]

I don't quite see it that way.

Your BMR calories are calculated based on your profile and are burnt at the same rate throughout the day and night. There are effectively a baseline and any activity adds to the calorie total.

If you are not wearing your fitbit you just get your BMR calories. If you wear your fitbit then you get BMR calories plus calories from tracked activity.

So, if you compare overnight calories wearing your fitbit against not wearing it then you might get a few extra calories tracked if you wear your fitbit if, for example, you had a few bathroom visits or were quite restless. 

[Nicwills]

Yea, didnt think of that. Thank you for your reply. 😊🤔