Fitbit Flex accuracy

NickHall1988

Hello everyone!

I have yet another maintenance question. How accurate is the fitbit flex?

So far I have only had it about one day. Yesterday it says I burn 3000 calories and walked 10 miles. (Which is about right, we went to a festival so I walked a mile, mile and a half, then 2-3 miles later in the afternoon, then since I'm sick and can't run I walked my running route which is 6 miles in length).

I ate 2500 of the 3000 calories it said that I burned because I am assuming that it is over estimating. I have it linked with MFP. I have it set to "Dominate hand" but wear it on my non dominate wrist and thus far have been removing it when not active. IE it's laying on my desk while working and I take it off for driving.

So the question is, should I be eating what it says I'm burning or should i be eating slightly less to be safe?

stuffinmuffin

I have the Fitbit Ultra and have had it for about 5 months. Mine is spot on, and yes, the calorie numbers look a bit fictionally high at first, but you'll be surprised to know - they're actually damned correct! I use mine to maintain and eat all cals burnt as said by my fitbit and I haven't gained an ounce of weight.

NickHall1988

Good to know, but if that is true I have been GROSSLY underrating. If I get 3000 cal just from walking, its probably a fair bit higher when I run the 6 miles instead of walking. This is also something I do pretty much every day with only small measures of deviation.

I think for the next week or so I'm just going to eat at a deficit from what my fitbit says and see what happens. I'm pretty full on 2500 calories anyway lol

Reevsie123

I have had the flex for a couple of months & find it pretty accurate, every now and again it goes a bit mad painted my deck and got 3000 steps !
When I am doing DIY and building work I put it in my pocket which works reasonably well. I only eat back about 50% of what I earn that way I know I am within tolerance of any errors

stuffinmuffin

I found from the Fitbit that I must have been undereating fairly significantly. I can tell you my moods have certainly levelled out and energy levels increased since eating my 'proper' amount. I wouldn't be surprised at the 3000 calories. I walk a lot each day and run a couple of times a week....I'm 107lb and maintain at an average of 2200 calories a day. : ) On MFP I was averaging 1700.

threshkreen

I was so excited when my Fitbit Flex came! In about one week, I was on the phone asking to return it. Unfortunately, for me, the type of exercise I do does not cause the Fitbit to register any steps or enough steps( I do weightlifting and treadmill walking at an incline). It does not take into account intensity. I was very disappointed because I thought it was a great idea.

Also, I hated always having it on - especially at night. I don't mean to put it down...it just didn't work for me, but I still think it is a great idea....I am just not suited for a pedometer.

WAHMto5

I have the Fitbit One and it is very accurate! I received it for Mothers Day and haven't missed a day without it since, love it! I do use the HRM for my runs though. I have found more then anything is a huge motivator for me to move more, especially on days that I see how low my activity it!

cgm117

I've had a fitbit flex for about 3 months and it seems to be very accurate. I find that it tends to be within 100 calories with MFP. I use to have a Nike Fuelband but I can do so much more with the flex.

ARoseinDecember

I just want in on this thread. Been wearing my fitbit nearly a year, but I never trust how many calories it tells me to eat. I'm in maintenance and it's putting me in 2200+ cals, depending, but MFP says 1690.....

judychicken

Bump

nxd10

I have had a fitbit zip since June, which I wear on my pants pocket. It does seem spot on EXCEPT for the things it doesn't measure - like bicycling. It also doesn't take into account arm heavy work - for example, I installed a ceiling a few weeks back and I know it underestimated.

As it says to do, I just add those activities in with the times into MFP, fitbit picks it up and subtracts those times out of its calculations, and everything seems fine.

I have been eating more and haven't gained anything.

macgyver_kit

This topic is getting a bit dated, but I'll jump in here anyway because I've just finished testing my Flex against a Yamax SW700 (reasonably respected "old school" pedometer).

This has been a fairly un-scientific test. Just for starters, I have to take the pedometer off at night so it misses a few steps each morning before I remembered to put it on. The time in the morning varied. If I got up early to a child or pet that was not expected, it was sometimes a while before I remembered to go and clip on the ped.

Anyway, I found the Flex surprisingly accurate. Certainly not "clinical trial" accuracy, but a good approximation to assist users in getting an idea of what they have been up to.

Based on all 32 days the Flex ended up counting just under 5% more than the ped. The average difference each day saw the Flex count about 10% more, although some days it counted a lot less. As I say, my test has not been overly rigorous, but the figures suggest to me the Flex is a more accurate indicator than it should be for a pedometer worn on the wrist. Accuracy could be further increased by removing it during rhythmic non-step activities (polishing a car, trying to start a stubborn line trimmer to use examples that threw mine out).

Here is my data for those that love the figures.

(By the way, sorry for the completely average formatting including the plain version at the very bottom. It looked ok in draft but then went all to pieces when I posted. I am too much of a gumby to work it all out. Directly below should be an image (captured from my original Excel doc) that shows up in a borderline way - although I'm afraid you will have to zoom right in with your browser...)





Date Pedometer Fitbit Difference % Difference FB (M)ore or (Less)
17/09/2013 8,315 8,461 146 1.74 M
18/09/2013 8,810 8,667 143 1.64 L
19/09/2013 11,409 10,210 1,199 11.09 L 19/9 FB on looser than usual, low batt by 6pm too
20/09/2013 7,759 6,436 1,323 18.64 L Intense day at office
21/09/2013 10,438 14,480 4,042 32.44 M Polished car while wearing FB
22/09/2013 11,063 9,366 1,697 16.61 L
23/09/2013 15,805 17,569 1,764 10.57 M Walking around Welly for meetings
24/09/2013 9,046 10,485 1,439 14.74 M Based at client offices - mostly presenting
25/09/2013 12,107 11,838 269 2.25 L
26/09/2013 13,110 12,353 757 5.95 L In court about 1/2 the day
27/09/2013 11,475 10,887 588 5.26 L
28/09/2013 10,147 9,562 585 5.94 L
29/09/2013 11,464 12,524 1,060 8.84 M
30/09/2013 12,968 14,980 2,012 14.40 M FB off c1 hour in am charging, then had FB on when trying to start line trimmer
1/10/2013 14,381 16,939 2,558 16.33 M Some work on line trimmer again. Also had FB only for time in the morning
2/10/2013 10,300 11,400 1,100 10.14 M
3/10/2013 11,052 11,178 126 1.13 M
4/10/2013 6,440 4,809 1,631 29.00 L Full on day at work
5/10/2013 15,673 16,091 418 2.63 M
6/10/2013 13,189 12,782 407 3.13 L
7/10/2013 10,190 11,124 934 8.76 M
8/10/2013 8,504 9,551 1,047 11.60 M
9/10/2013 6,917 7,212 295 4.18 M
10/10/2013 8,536 9,853 1,317 14.32 M
11/10/2013 10,645 10,303 342 3.27 L
12/10/2013 9,432 11,402 1,970 18.91 M
13/10/2013 13,155 12,296 859 6.75 L
14/10/2013 7,440 8,517 1,077 13.50 M
15/10/2013 Forgot ped today!
16/10/2013 Left ped hatch open by mistake before big walk - ped 6,294, FB 8,193 but result cannot be counted
17/10/2013 11,288 13,855 2,567 20.42 M
18/10/2013 8,771 10,192 1,421 14.99 M
19/10/2013 8,546 10,230 1,684 17.94 M
20/10/2013 14,378 14,199 179 1.25 L
N/A 342,753 359,751 16,998 4.84 M

Min % diff 1
Max % diff 32
Mean % diff 10.89

M:L FB More 19 vs 13 Less

Min steps diff 126
Max steps diff 4,042
Mean steps diff 1,155

nxd10

Here's a review of it:

http://pogue.blogs.nytimes.com/2013/01/14/the-fitbit-flex-improves-on-its-rivals/?_r=0

A NY Times review of accuracy of different monitors given different types of activity:

http://well.blogs.nytimes.com/2013/06/12/how-accurate-are-fitness-monitors/

I use a Fitbit zip to measure steps. It works well for me - at least as accurate as a pedometer. I use it to judge relative number of steps and to push me to hit 10,000 steps. I use it's calorie calculations. I say 'it works' because when I use those numbers and eat the calories back, I don't gain.

I teach statistics and am very interested in measurement error. This works well for the level of accuracy I need for this task. I do a lot of typing and hand movements, and that's what the flex over-counts, which is why I use the zip (and it was cheaper). I was looking at the new one and pondering using one as a watch.

macgyver_kit

Thanks nxd10. The Zip is a great choice, and the only reason I did not get one in the end was I worried about losing it or forgetting it in clothes that ended up in the wash.

In fairness to the Flex, I am not sure about what many people assume will be over-counting of typing. I work an office job, and spend a fair bit of time typing. First, my experience suggests that my Flex is not wildly over-counting generally, so that suggests typing is not playing havoc with my figures. Second, on two particularly full-on days at work (which I would have spent mostly typing, and typing frantically at that) the device actually counted over 1,000 steps LESS than the pedometer (20 September and 4 October on my spreadsheet).

What appears to throw the device out most is rhythmic arm activities like polishing or starting mowers etc (ie repeated motions along the same plane). And that cannot be a fault, because its exactly those sort of movements that the device must detect in order to track walking from the wrist.

Anyway, not sure it adds much, but thought I'd chip in because a lot of people ask about typing. Before I chose Flex I feared typing would throw things way off. My little experiment has allayed my fear, so the good people at Fitbit appear to have somehow designed the device to ignore typing.

nxd10

That's helpful. Some of the most energy intensive things I do around the house are things like cleaning out the chicken coop, which is exhausting. Flex would help with that. But I just log the exercise numbers.

I have lost a zip (although I really believe it was stolen). The new band that can work as a watch seems like it would work well.

Does anyone know if you can use two devices - some days a zip and some days a band? There are days when the band simply will not look great with my outfit. :blushing: