Calories burned without using Fitbit

[GypsyJude]

I forgot to wear my Fitbit the other day so it only recorded 312 steps but somehow it said I burned 3856 calories!! How on earth did this happen?

Moderator edit: Subject for clarity 

[RicardoFitbit]

Hi @GypsyJude, It's nice to see you again participating here in the Community Forums, welcome back! 

Thanks for bringing this to my attention. Fitbit devices combine your basal metabolic rate (BMR)—the rate at which you burn calories at rest to maintain vital body functions (including breathing, blood circulation, and heartbeat)— and your activity data to estimate your calories burned. If your device tracks heart rate, your heart-rate data is also included, especially to estimate calories burned during exercise. The number you see on your Fitbit device is your total calories burned for the day. 

Your BMR is based on the physical data you entered in to your Fitbit account (height, weight, sex, and age) and accounts for at least half the calories you burn in a day. Because your body burns calories even if you’re asleep or not moving, you see calories burned on your device when you wake up and will notice this number increase throughout the day.

Let me know if you have any additional questions.

[GypsyJude]

Did you read the message? Over 3000 calories burned!!!! 312 steps. And it has corrected to over 5000 now!! And it's 2 weeks ago LoL edit: I only wore it for about 20 minutes...