Fitbit question.

It sounds like a problem with your stride length. You can go into your Fitbit dashboard or app and enter a custom stride length.

First point: your stride is not actually always the same. If you are walking 'for fitness' its probably a longer step than if you are wandering around a grocery store.

But for fitness, you can adjust until it seems more accurate. Figure out how much it gives you for a treadmill walk, then adjust. Such as if you walk 1 mile on the treadmill and Fitbit shows you walked .8 miles, then increase the stride by 2-3". Repeat as needed. If it gets closer you're on the right track. If you adjust 3" and then its giving you too much distance, then take 1" off.

As to whether or not its counting all your steps? Depends on the type of Fitbit and you. If its a wrist device and you're holding on to something it probably is not counting all the steps. In my experience the Fitbit One is the most accurate as it recognizes trunk movement rather than hand movement.

A track at a local high school is a good place to calibrate many fitness trackers