Fitbit Exercise Tracking is Confusing

I’ve had a Fitbit Zip for almost three years and I use the iOS app to sync the data from it. This app lets you track exercise that wasn’t captured in full by the step counter. I use this to add info about weight training and aerobics at the gym.

The active minutes, steps, and distance often do not add up when I add one of these exercises manually. The other day, I took a moderate 1 mile walk but forgot to start the tracking feature in the app. After my walk, this is what my activity looked like.

screenshot of fitbit app showing 24 minutes of activity, 5319 steps, 2.26 miles
Fitbit activity before logging exercise

My stats showed

  • 5,319 steps
  • 2.26 miles
  • 24 active minutes

After I added in my walk manually, the stats updated in an unexpected way.

screenshot of the Fitbit app showing 5,796 steps, 2.45 miles and 0 active minutes
Fitbit activity after adding a walk

My stats changed to

  • 5,796 steps
  • 2.45 miles
  • 0 active minutes

What? I can’t figure out what Fitbit is trying to do when I log exercise manually. The distance and steps shouldn’t change when those are precisely what the tracker tracks. My active minutes dropping to 0 is what I find most perplexing. How would adding exercise ever reduce active minutes?

By way of comparison, here are my stats from yesterday before and after manually logging 50 minutes of aerobics.

side by side screenshots showing discrepancies between calories and active minutes
Fitbit comparison when logging aerobics

Here we see the number of calories burned dropped by 102 while active minutes increased by 10. Again, what? I wasn’t able to find any information from Fitbit about how its software calculates these numbers but I think it’s safe to say, something doesn’t add up.