Resting Calorie burn calculation

[viv_123]

I am using a pixel watch. 

Recently, I have been trying to figure out my Calorie burn rate. After some research, I realised that fitbit data doesn't provide a segragated active and resting calorie. It always adds up to the predetermined resting calorie rate. I believed this pre-determined calorie was based on some Harris-Benedict formula which uses height, weight, gender and sex of the person to calculate the Resting Calories burned.

After analyzing my data of one month, I realised that the resting calorie has dropped a bit(around 100 calories per day). Even though the the weight and height parameters have not been altered, the resting calories showed a decreasing trend.

Can someone throw light on the Resting calorie calculation used by fitbit/pixel watch devices?

Is there any parameter that I am missing in the resting calorie calculation?

[ManuFitbit]

Welcome to the community forums @viv_123. 

Thank you for taking the time to share all this information regarding calories. 

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.

Note that in certain regions, you see kilojoules instead of calories. To change your units of measurement, see How do I change the units of measurement in my Fitbit account?