Biking HELP! fitbit or mfp cals?

sijomial

Both your numbers look very high for 31 minutes, 821 sounds impossible and 449 sounds improbable.

If you give up the idea that you can ever be accurate unless you are prepared to invest in a power meter (not worth it IMO for a non-serious cyclist) then you come down to trying to find a reasonable, consistent and personal estimate.
I've tried a few!

MFP's "Bicycling, 16-20 mph, very fast (cycling, biking, bike riding)" category - far too high to be possible.

Next is a group all around similar and reasonable numbers (for me remember):
Runkeeper (free app)
MFP's "Bicycling, 14-16 mph, vigorous (cycling, biking, bike riding)" category - although I'm riding faster than that.
Polar FT7 HRM (fairly basic model)

On the lower end of the calorie scale and probably more accurate:
Polar FT60 HRM - (more advanced model with VO2 max setting) - about 10% lower than above group.
Strava (free app)
Garmin bike computer with HRM

BTW - I managed to lose and maintain my weight using the FT7 HRM despite it probably being a little too generous, I simply adjusted my calorie intake to give me the desired weight result over time.

AJ_X1

MFP should be correct one. Fitbit fails to register biking correctly.
Heart rate monitor can help to get better.

But these calories are indicative only. Actual calorie burned can be higher and lower depending on various other factors, like room temprature etc etc.

dazwan

I use a mixture of Runkeeper (as it syncs automatically with MyFitnessPal) and strava, if you don't have gps, you can even plot out your route on the map in runkeeper and enter your hrm data. I just upload tcx and gpx files from my computer and let it do the rest.

To get strava to sync workouts with MFP I've been using tapiriik (https://tapiriik.com/) you can sync strava with runkeeper + a few others (so you can keep synced with mfp via the back door). It does mean having accounts for everything, but you only ever need to enter your workout data once.

I find my calorific burn on the bike is usually in the region of 15 cals/minute, so a 30 minute burn gives me approx. 450 calories. That's a steady effort, usually averaging around 135bpm.

If you're doing road, then I've seen people on strava regularly report doing sections in the high 20's, not sure about sustained though but I for one don't doubt anyone is capable of this, the pro's can do this for hours (even in time trials with no peleton to hide behind). I wish I was that fit/aerodynamic! On a run I usually average approx. ~16mph on a long ride with ~20mph on the flat sections (unless there's a strong headwind). I ride a cyclocross, so the extra weight, wider tyres and lower gearing all add up to a slower package, maybe next year I'll look to invest in a new shiny road bike that weighs half as much as my commuter.

To answer the original question though, go with your HRM, as long as you've entered your stats correctly (age, weight, gender, etc) then it will likely give the most accurate estimate of calories burnt as it has the best measure of your efforts. If you have the funds invest in a decent computer that will work with your HRM strap (some straps use ANT+ or even Bluetooth to connect) and also add a cadence/speed sensor, this will collate all your info to give a better picture of how you are performing. The better computers will then allow you to sync all this data in Strava or Runkeeper and then you will know what you have is as accurate as you can get. Of course you could also invest in a Bluetooth HRM strap and candence sensor and run Strava/Runkeeper on your smartphone, just try not to cry too much when you fall off and break your phone on the tarmac or get it wet in the rain.

KarenJanine

I find that logging cycling via fitbit gives a much closer estimate to my HRM reading than MFP. On this occasion I would recommend recording cals via fitbit. But as others have stated, you may want to look at different app / devices for future reference.