iPhone Step-Tracking Inaccurate vs Pedometers: UBC Study

According to a recent study by the University of British Columbia, the iPhone’s built-in pedometer missed about 1,340 steps during a user’s typical day when compared to a dedicated wrist-worn accelerometer. “In order to make accurate conclusions, we as researchers need to know that the data is actually representative of real behaviour,” said Mark Duncan, the study’s lead author.


33 participants were involved in the UBC study, which was divided into two parts i.e. a laboratory test and a test in regular living conditions. In the lab test, participants carried two iPhones, a personal iPhone and a shared one provided by the lab, which would allow researchers to see if different phone models produced different results. Participants walked on a treadmill for 60 seconds at various speeds and their steps were counted manually. 

Personal iPhones underestimated steps by 9.4 per cent at the slowest speed of 2.5 km/h. The shared iPhone fared slightly better at 7.6 per cent. At faster walking speeds, the phones were off by less than five per cent, which is generally considered acceptable for a pedometer.

For the other part of the study, participants fixed accelerometers to their waists for a full day, and recorded step readings from the iPhone at the beginning and end of the day. Over three days, the iPhone underestimated the accelerometer data by an average of 21.5 per cent, or 1,340 steps per day.

“The accelerometer in the iPhone actually does a pretty good job when tested under lab conditions,” said senior author Guy Faulkner. “You just have to have it on you at all times.”

Duncan however stressed that an average person shouldn’t be discouraged from using health apps for motivation. He added that people who are already tracking their steps, they can rest assured that if their phone says they’re getting the recommended 10,000 steps in a day, they are probably getting at least that many.

The study was published last month in the Journal of Sports Sciences.