I have started using MapMyRide.com to keep track of my bike rides as a motivational tool to keep riding and improve my health and fitness.

However, when comparing the calorie counter from various sources on the 'net with the one used on MapMyRide, the MMR one is about 15-20% lower.

Anyone else discovered the same?

On the other hand, perhaps I could ask myself, should I even bother thinking about it?

What are people's thoughts about Strava? My commute (~30 mins moving time at ~16-20mph) burns ~300Cal on Strava but using, say, livestrong I burn 600 cals...

all the people I know that count calories are fat.

Assume 500 calories per hour and you'll be in the ball park.

Well I definitely do not skew your sample set then..

MMR and other apps like that don't really know how hard your body is working, how much you're coasting, etc. I think an actual heart monitor, properly set to your age/weight, etc, will at least get you closer to the ball park.

Or have been, and count to keep from getting a fat again.

On RunKeeper if I enter my data manually (time and distance) I 'burn' about 1000 calories/hour, if I download the ride with a gps it's about 600 cal/hour so I don't rely on those number ever, instead I keep on being fat.

Most calorie counters/GPS apps tend to overstate how many calories you're expending while biking. I've heard around here a more reasonable estimate is 30-50 calories a mile, depending on your size, ability, speed, etc.

Probably the best measurement of energy used while biking is a power meter on the crank. Guestimating via your speed or heart rate will probably introduce some error. (not to poo-poo heart rate monitors, they are useful, but for energy use there are better measurements)

The calories burned in MMR is purposely made to be 15-20% lower than reality too make you feel like you didn't ride long enough. That's another motivator.

If you want accurate "calories burned", get a garmin 200 or above. It also has a lot more stuff than just MMR.

I'll second the garmin!

I've got the 310xt and the difference between calories burned using the HRM and when I don't use the HRM is huge. For example, a just under two hour 50 km loop where I *didn't* use the HRM says that I burned 1180 calories. Another ride where I did use the HRM is on the same loop (but minus an out and back): an hour and a half, 38 km, and 420 calories. I highly doubt that my last 10k on that first ride burned 720 calories.

I'm guessing that speed-based calorie calculators don't consider that downhill = fast.

Or people who just really like numbers