Do you use a fitness tracker to monitor your levels of physical activity and keep an eye on how many calories you’re burning from day to day? If you do, you could be relying on overestimated information, according to the findings of a new study. Researchers at Aberystwyth University in Wales found that many popular fitness trackers often overestimate the number of calories burned while walking by over 50%. In fact, all products tested by the research team ranging between £20 and £80 in price were inaccurate during walking and running tests. Surprisingly, some fitness trackers gave polarising results. For example, the Fitbit Charge 2, the best-selling fitness tracker on the market, scored very well when it came to estimating calories burned while running, underestimating by just 4%. However, when measuring walking, the same device overestimated calories burnt by more than 50%. Other less expensive devices, namely the Letscom HR and the Letsfit – significantly underestimated the number of calories burned while running by 33% and 40% respectively. However, both were more accurate than the Fitbit Charge 2 in estimating calories burned while walking, overestimating by 15.7% and just 2% respectively. One of the researchers, Dr Rhys Thatcher, said that while fitness trackers can be great as motivational tools, people need to be cautious in the data they provide. “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 said.