Is Fitbit this inaccurate?

It is about the calories. You're experiencing completely normal water retention and weight fluctuations. How recently have you started working out? Muscles are particularly prone to retaining water when they're sore and rebuilding. Expect to gain for 2-3 weeks after starting a new lifting program.

Are you female? If so, those weight fluctuations will also be tied to your monthly cycle. Massive water retention around your period.

Weight loss is not and never will be a straight line. There will be ups and downs and there will be periods of weeks at a time where you lose nothing - and then all the weight you should have been losing will come off at once in 3-4 days. It's because water gets stored in your empty fat cells as the body waits to see if the cell will be refilled before downsizing. Don't stress the day to day, or even the week to week. The longterm trends matter.

This is my weight log for the last two months. Look how I don't lose anything for 2 weeks at a time, and how rapidly it starts going down after the stall is broken.

That Excel spreadsheet you're seeing you can find here. It calculates your true TDEE based on weightloss compared to calories in. I compare it to my fitbit data and for what it's worth, fitbit overestimates by about ~10%.

Last but not least - do you own a food scale? Because this is where most people fail CICO. How accurate is your calories in tracking? Do you weigh your portions? Do you log those small snacks here and there? Do you log the oil you used for cooking? Etc. All those small things can add up in a big way.

/r/fitbit Thread Parent Link - i.imgur.com