You finish a run feeling fantastic. Then you check your smartwatch. Your fitness score has dropped. You burned hardly any calories. Your recovery score is terrible. The watch tells you to rest for the next 72 hours. The worst part? The run felt amazing.
So why is your watch telling you the opposite? Ultimately, because smartwatches and fitness trackers aren’t always accurate.
For nearly a decade, wearable fitness technology has been one of the top exercise trends worldwide. Millions of people use these devices daily to guide their health and fitness decisions. Smartwatches provide data on calories burned, fitness levels, recovery status, and readiness to exercise again.
But here’s the catch: your smartwatch doesn’t measure most of these metrics directly. Instead, many common readings are estimates. And estimates are not the same as facts.
Calorie tracking is among the most popular smartwatch features. However, its accuracy leaves much to be desired. Research shows wearable devices can under- or overestimate energy expenditure—commonly displayed as calories burned—by more than 20 percent. These errors vary depending on the activity. Strength training, cycling, and high-intensity interval training can produce even larger inaccuracies.
This matters because people use these numbers to make real decisions, including how much to eat. If your watch tells you that you burned 500 calories when you actually burned only 400, you might eat more than you should, undermining your fitness goals. Conversely, if it underestimates your burn, you might undereat and lack energy for recovery.
Beyond calories, metrics like “readiness scores” and “fitness scores” are often based on algorithms that combine heart rate variability, sleep data, and other inputs. While these can provide helpful trends, they are not medical-grade measurements.
So, what should you do? Use your smartwatch as a general guide, not an absolute truth. Pay attention to how you feel—just like that great run that your watch didn’t approve of. Sometimes, your body knows better than a wrist-worn computer.
