Your Smartwatch Is Mendacity About How Many Energy You Burned

After a tough exercise, checking your calorie burn and mentally budgeting dinner round it appears like affordable math. It isn’t. A Florida International University examine revealed in PLOS One in July 2026 examined 4 standard smartwatches in opposition to a COSMED K5 — a lab-grade metabolic analyzer that measures precise oxygen consumed and CO₂ exhaled — and located each system considerably misestimated energy burned throughout biking. Error margins ran roughly 15–25%, with some units averaging a lot greater. “You can’t treat the calories burned number it gives you as an accurate number, because it’s not,” stated lead researcher Jason Kostrna.

The setup concerned 58 adults using train bikes whereas sporting 4 units concurrently:

Device	Avg. Overestimation
Apple Watch Series 8	~21.6 kcal
Samsung Galaxy Watch 5	~56.8 kcal
Garmin Forerunner 955	~68.6 kcal
Fitbit Sense 2	excluded*

*Fitbit Sense 2 was a unique drawback solely — it generally logged a single calorie for a complete exercise, forcing researchers to exclude most of its information from the first evaluation as a consequence of reliability issues.

“You could be off hundreds of calories each week and easily end up in a calorie surplus when you think you’re in a calorie deficit.” — Jason Kostrna, FIU

The Problem Gets Worse Depending on Who’s Wearing It

The folks most definitely to trace energy for weight administration are, considerably cruelly, getting the least correct numbers.

Error magnitude elevated as physique fats proportion rose, in line with the PLOS One paper. That means higher-BF customers — usually these most motivated to trace energy for weight administration — are working with a few of the shakiest estimates the watch produces. The algorithms powering these units are proprietary, educated on datasets the businesses received’t disclose publicly, and apparently not constructed to deal with various physique compositions persistently. Nobody outdoors the producer is aware of precisely what assumptions are baked in.

This isn’t a brand new drawback. Think of it like Waze confidently rerouting you — coronary heart price information arrives reliably, like correct turn-by-turn instructions, however the calorie estimate is the ETA that retains mendacity. Prior analysis suits the identical sample:

• A 2016 PLOS One examine discovered coronary heart price errors inside 1–9% throughout units whereas calorie errors ranged 9–43%.
• A 2022 examine discovered Apple Watch and Garmin overestimated strolling vitality burn by 20–32%.

The FIU findings match a decade-long sample the trade has but to meaningfully clear up.

Stop Trusting the Number. Start Using the Trend.

Your watch is a helpful compass — deal with it like one, not like a laboratory instrument.

Kostrna’s workforce recommends shifting focus to coronary heart price zones and long-term patterns reasonably than single-workout calorie counts. If you’re planning meals consumption round your burn quantity, spherical it down and keep away from aggressively slicing meals primarily based on one session’s readout. Your physique nonetheless wants sufficient gasoline for restoration and constant coaching.

Kostrna’s subsequent analysis part targets power coaching calorie accuracy, the place quick, intense bursts make algorithmic estimation even more durable. Expect the numbers to get messier earlier than they get sincere.