How does Fitbit track bike calories with Versa 2?

[jflartner]

I have a Versa 2 and I ride an ebike to and from work. I use the Bike exercise mainly so I can track how many calories I'm burning. 

Although my heart rate does get up there, because it's an ebike I'm concerned that fitbit is including my speed (which is partly me pedaling and partly the motor assisting) as part of the calories burned calculation. 

I ask because just based on my past experience tracking food calories in and exercise calories out, I'm pretty sure based on the effort I'm putting out that fitbit is giving me too many calories for my rides. Although it could just be that I'm not calculating where my BMR number should be in the morning and afternoon.

If I'm mainly concerned about calories burned during my rides, would it be more accurate for me to use the stationary bike activity on my watch? I do like having the GPS data to send to Strava, but it's not necessary. 

Thanks!

Moderator edit: updated subject for clarity. 

[JohnnyRow]

Calories burned should not be paying any attention to distance or speed, but just be based on your heart rate to judge how hard you are working.

[AndreaFitbit]

Welcome to the Fitbit Community, @jflartner. Thank you for sharing your question regarding calorie burn on biking activity.

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. Your heart-rate data is also included, especially to estimate calories burned during exercise. 

As @JohnnyRow mentioned, calories don´t pay attention to distance or speed. 

Keep on visiting the forums.