Watch Calorie Accuracy: Why Garmin, COROS, and Apple Watch Overestimate Burn
Watch: 820 kcal. MET math: ~700. Treadmill: 590. Same 10 km. For Garmin, COROS, and Apple Watch, the device total is often the highest — and the weakest number for precise nutrition. Wearables are useful for trends; mediocre as receipts.
Active vs Total Is Half the Trap
Calories are modeled from profile data, movement, heart rate, and proprietary engines. Confirm active vs total — Garmin totals often include basal burn during the activity window. Logging “total” as “active” invents snacks you did not earn. Background: How Many Calories Does Running Burn?
Worked Comparison: 70 kg, 10 km in 55 min
Distance rule ≈ 70 × 10 = 700 kcal. MET (~10.5): Calories/min ≈ (10.5 × 70 × 3.5) / 200 ≈ 12.9 → ×55 ≈ 707 kcal. Optical-HR-high watch may show 820–880. Planning number for a cut: ~700, or ~15–25% below the watch if it exceeds MET. Run sessions through the Running Calories Calculator. HR-driven error modes: Garmin vs COROS HR accuracy.
A chest strap usually reduces HR-driven calorie error; it does not remove proprietary bias or active-vs-total confusion. Still compare to MET. Do not eat back every watch calorie during a cut.
Make Wearables Useful Anyway
- Update body weight when you change ~2+ kg
- Prefer a chest strap on key workouts if calories inform eating
- Stick to one ecosystem for weekly sums
- Treat pace, distance, and HR zones as the strong fields
Steady Runs Are Best-Case
Expect wider errors on intervals, trails with hiking, strength/metcons, heat drift, and wrong body-weight profiles. Steady Zone 2 with a chest strap and correct weight is best-case — still treat about ±10% as noise when planning meals around a single run.
Weekly Trend Beat Single Runs
Use one ecosystem’s active calories for week-over-week comparisons, not brand-hopping. Recalibrate expectations after heat waves, firmware changes, or a body-weight update. Rings closing are motivation tools — they are not metabolic lab reports for meal planning.
Decision Rule
If watch calories exceed MET/distance estimates by ~15% or more, plan food from the lower MET/distance number (or a haircut of the watch), especially in a cut. If watch and MET agree within ~10% on steady Zone 2 with correct weight, either is fine for weekly trends — still judge by multi-week weight and performance.