Accuracy of calories burnt for charge HR

[Telly2]

Hi

I'm new to this forum today and have seen references to the accuracy (or rather non accuracy) of the calorie count.  Could someone please explain this to me or point me in the direction of a good summary discussion.  Thanks

[Dominique · Accepted solution]

I don’t think it’s possible to present anything else than empirical evidence that for any given person, some trackers may underestimate energy expenditure, while others may overestimate it. We know that there is a margin of error when estimating calories out with a fitness tracker. If we want to use our Fitbit for weight management, we need to establish what that error is in our particular case. This can be done if you’ve been tracking both your intake and your weight for long enough (at least 3-4 weeks). Let’s say you’ve had an average daily deficit (according to your dietary intake estimated by you and your energy expenditure estimated by your Fitbit) of 500 calories, but you haven’t lost any weight at all in two months time: then you would know your Fitbit overestimates your expenditure by 500 calories. Or let’s say your average daily deficit was 750 calories (which should result in a 1.5 lb weekly/6 lb monthly loss), but you’ve only lost 8 lb in two months time: then your real deficit was 500 and your Fitbit overestimated expenditure by 250. Given that you’ve had your Charge HR since November 2015 (if it was your first Fitbit), you should have some idea about the accuracy of calories burned if you have been tracking your intake and your weight during some period of time.

For tracking your weight and eliminating the impact of daily fluctuations, it can be useful to use TrendWeight (see link in my signature), which you may have seen mentioned by several contributors to the community.

You may also want to double-check calories burned using an online calculator such as this one. It will give your BMR (using the same equation as Fitbit). Your average step count is a pretty good proxy for your activity level, according to the five standard levels used by the calculator. If you see calories burned reported by your Fitbit are much higher than what you would get with the "high" activity level, chances are they’re being overestimated (unless you’re having a crazy high average step count, like 25-30k+).

[GershonSurge]

I find my Surge, Zip and Charge 2 are all about 98% accurate in counting calories even though they all indicate I burned a different number of calories each day. To see why this is true, one has to understand calibration error. For example, a car speedometer that consistently indicates 10% high is not inaccurate. One simply has to subtract 10% from the indicated speed to get the actual speed.

To determine the calibration error, a person has to meticulously track calories consumed. This means weighing every item of food and logging it -- even that single potato chip a person eats during the day. 

I prefer tracking the total calories consumed and the total calories burned since the start of losing weight. Divide the total deficit by the total weight change, and you can determine how much of a deficit it takes you to lose weight. After about 25 days, I find the number remarkably consistent. With my Zip it's about 2,900 calories. With my Surge, it's about 3,800 calories. With my Charge 2 it's about 3,500 calories. Each device has the same accuracy, but they have different calibration errors. (Note: This does not work with total weight changes close to zero.)

There will be the odd day where a person suddenly gains or loses 5 pounds for no apparent reason. In a few days, the effects of the outliers will diminish. 

Practically speaking for a person new to losing weight, I suggest eating an amount equal to the Basal Metabolic Rate (BMR) every day unless the deficit will be more than 1,000 calories. If they feel weak or dizzy, I suggest eating a bit more. To keep it simple, get 10,000 steps every day and don't worry about the calorie deficit. This amount of exercise will burn enough calories and most likely prevent hunger pangs except when it's time to eat. Addictive cravings to fat, sugar and salt are a different challenge. 

Suggestion: If you make all the information on your profile public, it will be easier to answer questions in the future.

[DavidSchneier]

You've already received some good advice and insight, but I wanted to share that each individual is different and FitBit can't easily detect how/why. I find that if I subtract 700 calories from the estimated deficit shown by FitBit it closely mirrors my actual progress. This can be explained in part by my having hypothyroidism (which slows the metabolism even though treated) and also my likely not tracking calories consumed as accurately as I'd like to believe. 

From experience, I've learned that by maintaining my current activity levels I can eat around 2,200 calories per day and not gain/lose weight; FitBit thinks that number is closer to 3,000.

[Telly2]

Thanks very much for the explanation and the links.  They were really helpful.  Thanks to the others who took the time to reply also.