If you've been on a health kick and you've been relying on your fitness tracker as your best friend, then you may have to think again.
They've become incredibly popular in the last little while, amongst fitness fanatics and people who are just trying to be a little healthier.
However, they may not be all that accurate.
The good news is if you're using your tracker to record your heart rate, then you're probably okay.
Stanford University of Medicine conducted a study, which included a number of different fitness trackers among 60 participants.
The study found that six of the devices measured heart rate with an "error rate of less than 5%".
But for counting calories and recording your energy output, it's a different story.
The most accurate device in the study was incorrect by a huge 27%, with the least accurate incorrect by 93%.
The study also noted that skin colour and BMI can affect the tracker's performance.
The researchers concluded that if you want to use your fitness tracker to measure your heart rate, you're good to go. Anything else is very likely to be dodgy.