When you splurged on that fitness tracker last year, you probably expected it to accomplish the most basic tasks: check your heart rate, monitor how many calories you burn, and record your (many) hours of beauty sleep. At least, that's what you were promised when you unwrapped your shiny new watch.

Recent research shows, however, that fitness trackers aren’t very good at judging how many calories you’re burning every day, despite their claims.

At Stanford University, researchers studied 31 women and 29 men, and a total of seven different devices—Apple Watch, Fitbit Surge, Basis Peak, Microsoft Band, Mio Alpha 2, Samsung Gear S2, and PulseOn. The participants did what any normal person would do, such as run on the treadmill, cycle on the exercise bike at the gym, or sit still at their desk. After comparing all this data to "gold standard" laboratory-based measures, they found that fitness devices were generally falling short when it comes to accurately calculating your calorie expenditure.

The results were published in the Journal of Personalised Medicine, showing that the lowest rate of error was 27.4 percent in the Fitbit Surge and the highest was 92.6 percent for the PulseOn tracker.

According to Ashley, errors in calorie counting could arise from a number  of factors, such as low-performing algorithms or incorrect data input by users. Whatever the case may be, Ashley thinks this might be affecting certain lifestyle choices of individuals who are relying on their fitness trackers.

There’s good news, though. Your fitness tracker is likely very good at recording your heart rate.

The Apple Watch only had a median error rate of 2 percent, while the highest error rate, which came from Samsung Gear S2, was 6.8 percent.

Ashley still believes these devices hold a positive place in our life, since they inspire us to pay "more attention to diet and exercise." It's important, though, that you're not basing your meals on the data from your last workout. Just maintain a healthy, sustainable diet, no matter how many calories your Fitbit said you burned.