If you've been frantically checking your fitness watch while you try to burn off those holiday treats, we have some bad news for you.
A new study out of Wales claims that Fitbits and similar fitness trackers are dramatically overestimating the calories burnt during exercising.
Researchers at Aberystwyth University tested various fitness trackers, varying from NZ$40 to $150 in price.
They found that the Fitbit in particular overestimated the calories burned during walking by more than 50 per cent.
The study also shows that while less expensive devices, like the Letscom HR and the Letsfit, were more accurate during the walking test, they overestimated the total during running by 33 and 40 percent.
The research follows warnings that fitness trackers inaccurately estimate the amount of weight lost following exercise, particularly for overweight people.
Lead researcher Dr Rhys Thatcher told the BBC that fitness trackers had an "inherent tendency" to over-measure.
"If you want to know the exact number of calories that you are burning during an exercise session then it doesn't matter which device you use, you have to interpret the data with some caution," he added.
A spokesman for Fitbit told the Telegraph: "We do not claim to be scientifically accurate at the number of calories being burned."
Letscom and Letsfit said they could only give estimations based on data inputted by users such as height and length of stride, but again maintained the trackers were not scientific devices.