How does Fitbit count calories for a workout?

[cmookbridgman]

My Fitbit is not synced to MyFitnessPal, because that was just incredibly confusing. I wanted the Fitbit because I wanted an accurate calorie count on my exercise, rather than just going with MFP's very rough estimate. But, for instance, I just walked an hour at a brisk pace (I am a 144 pound woman), and my Fitbit told me I had burned 457 calories. That is nonsense. MyFitnessPal said 260. I plugged in my numbers on two other websites, and both gave me something that roughly matched MFP. What I want the Fitbit to give me is actual calories burned for a given activity, not an adjustment to a daily calorie goal. HELP!

[emili]

It depends which fitbit you have. If you have one that has HR then your calories are based on the HR for that activity. If you have one without, calories are estimated using your weight similar to how a treadmill or elliptical does it. I am 132 pounds and when walking for an hour briskly, my HR doesn't go below 100 BPM, I burn 350 calories +/- 20 calories depending on my actual HR. So your HR maybe slightly overestimated, but not terrible. Nothing but a chest strap will give you the accuracy you are looking for. All calorie burn is almost right, but it is consistently almost right so you can still plan your deficit and see results. 

[Heybales]

Exercise is done with HR-based formula for calorie burn.

Your other sites if they used weight and pace, or distance and time - were more accurate. Shoot - manually log it on Fitbit as Workout Record after the fact - you'll get the same well calculated calorie burn. I'd take it.

It'll overwrite whatever Fitbit came up with via HR, but you can leave the Activity Record to view the other stats - HR, distance, steps, original calorie burn.

Walking and running is more accurate via distance-based formula, but for some activities HR-based is best estimate - even if pretty rough.

Fitbit has your restingHR, but it's estimating your HRmax (rather important, did you avg 140 of 160 max, or 200 max for instance), and your VO2max, from other stat's (BMI and amount of workouts).

But even if you had measured HRmax and VO2max stats to put into a formula - HR can be inflated for cooling purposes, stress, dehydrated and thick blood, ect.

And is only a valid estimate for steady-state aerobic - not intervals, not sub-aerobic (like daily life) or anaerobic (like sprints), and not the upper & lower ranges of the aerobic range (like walking or running max speed).

So if this is new usage, your Fitbit may still be adjusting to your stats, and until then - suggest manually logging the walking & running and take the suggested calorie burn.

Remember too, MFP was receiving from Fitbit your Daily calorie burn in total, not just exercise, actually not even exercise, just total.

That allowed MFP to correct itself fair it's estimate of daily burn based on your guess of 4 activity levels.

You could be way more active than your guess - and that daily burn counts.

Deficit should come from best estimate of what you burn in total for the day (or on average), not starting at low level which allows little movement lower when needed.

[cmookbridgman]

I have a sneaky suspicion that if I assumed I had burned 457 calories on
that workout rather than 260, I would allow myself too many additional
calories for the day (keeping to 1200 is HARD). I wouldn't eat *all* those
calories, obviously, but probably too much. I lost 20 pounds following
MyFitnessPal's estimates two years ago, so I guess I will stick with that.