Did you know there are about 20 million fitness trackers being used in the US right now?

Fitness trackers which count your calories and your steps, like the Fitbit, are a growing trend that isn't showing signs of slowing down. But how accurate are they?

"Well, there are definitely a lot of great benefits to having a fitness tracker," said Dr. Penny Bowen.

Unfortunately, Bowen has also seen an uptick of patients wearing trackers coming in with injuries.

“They can definitely push people beyond their limits," Bowen said. "So at EVDI medical imaging, I actually see patients with more sports-related injuries or stress-type injuries, where they push themselves beyond their limits and they have an injury as a result of that.”

You'll be glad to hear trackers are more than 90 percent accurate in measuring steps. However, they're not as accurate in counting calories.

"[They're] either off in too many calories burned or not enough calories burned -- anywhere between 30 and 50 percent, there’s a great range. So you can’t really rely on them for an accurate measure of how many calories you burn, but more of a general gauge of how active you are," Bowen said.

Another piece of advice? Studies show trackers that monitor heart rate are more accurate.