How accurate are your Fitbit calories?

Keep in mind what information the fitbit is collecting. How often your arm moves, the rate of movement of that arm, and your HR. With that limited data it cannot be perfectly accurate for determining energy consumed. Correlating that data to distance is not overly complex. Energy consumption is much more challenging because it involves the fitness level of the subject, energy on board, and other factors. The device is using that data and the results from heaps of scientific studies to try to give you the calories consumed based on your personal stats. When it comes to energy consumption we are all somewhat of special snowflakes. That is why some stay thin easily, and some pack on the LB's. I think 20% could be a reasonable target. A great device, but it needs to be calibrated for an individual based on tracking over a period of time.

From Fitbit site:


In case interested here is a report to achieve how the energy consumption can be measured for an athlete where a high degree of accuracy is necessary: https://pdfs.semanticscholar.org/751c/7b4dec47f8c5da324f2b782df837dc33bf77.pdf

Abstract:

GottaBurnEmAll wrote: »

It should be noted that Fitbit measure jolting or impact, not casual arm movement.

If you applaud with it on or shake out laundry, it will measure that as steps, for example. There needs to be some impact accompanying the arm movement for it to register as a step.

This is why I've started taking mine off while doing the washing -_- was giving me too many steps

Lets consider this in perspective shall we?

You are wearing a relatively inexpensive mass produced consumer device that is calibrated to be close for a wide range pf people in your age/gender/weight range. This device uses proxy measurements to determine calorie burn rates. Steps are measured by arm movements and jolts, calorie burn rate is measured in part by heart rate.

Lots of places that errors can creek into the calculations but you then compare the results to high end scientific equipment that takes trained technicians to operate and produce results, individual tests will cost you more than your fitbit.

IF that gives you results in about 10 to 20 percent of actual then I’d say that is pretty good.

I use my Fitbit to ensure that I achieve my minimum desired burn, not so much in the actual calorie burn shown but to compare today with yesterday with tomorrow. A higher number one day means I burned more calories than the previous day. This is only accurate as long as I am doing similar exercises. I get a indicated burn of 300 calories for a brisk 30 minute walk but only 200 calories for a 30 minute fast swim. Obviously a swim ay will have lower indicated calories than a walking day even if the actual burn is identical. I take that into account when comparing swim to walk days.

Of course we then compare the indicated burn rate with our logged calorie intake. Remember that the labeled nutrition numbers can be out by 20% according to a very toothless law. There is no penalty for any food manufacturer misstating the calorie content in their foods.

If we are using raw foods, how many calories in an apple? In an egg? If you look at the MFP numbers they are all over the map. Even using the US government official numbers there is room for some variation, how big an egg or apple? Even same sized eggs and apples will have different nutritional contents depending on what the chicken ate or what variety of apply you have.

I simply use the numbers for either food or burn as a rough guide knowing that there are numerous sources of errors in them , some of which I know and can adjust for some of them I don’t know or don’t have any idea of the magnitude or direction of these errors.

I take the indicated burn and subtract 10%, I take in calculated food intake and add 20%. No real reason for these numbers but in my case they seem to work. I then aim for a 500 to 750 calorie gap and that comes close to my actual weight loss over time. ( i.e. a kg every 10 days to 2 weeks or so)

Remember the scale also has lots of errors in it so I simply use the 7 day moving average for weight, muscle mass and body fat composition.

All this is just to assist in reaching my desired goal and that is to like what I see in a full length mirror every day. That is the only result that I really care about, everything else is simply to assist me in getting there.