# Energy expenditure, device

The watch’s calories-burned figure. Excluded from the TDEE engine: in a laboratory test of seven wrist devices, median errors ran from 27 to 93%.

Type: biomarker · Unit: kcal/day · Domain: Nutrition & Energy Balance · Accuracy: Estimate · Importance: Context

Also called: calories burned, active calories, watch calories, Apple Watch calories, Garmin calories, energy out

## In one sentence

The calories-burned figure your watch or band reports, which VT keeps as the device's number and does not use for anything that involves food.

## Why it is kept

It is a series people have followed for years, and as a trend on one device it says something about how much you moved. It is also the figure that sits beside the energy-sources split on the activity sheet, where it carries the device's error.

## Why it is not used

Because it is not a measurement. A wrist device estimates energy from heart rate, movement and your profile through a model it does not publish, and when seven wrist devices were tested against laboratory calorimetry in 60 volunteers, their heart rate came within 5 percent but their energy-expenditure error ran from 27 to 93 percent, and no device came within 20 percent (Shcherbina 2017). An error of that size is larger than any deficit a weight-loss plan would set, which is why the TDEE engine excludes device calories entirely and builds its estimate from your weight and your log instead.

## What moves it

Movement and heart rate, through the maker's model; also the maker's firmware updates, a change of wrist, a loose strap and a cold day, none of which change what you burned.

## How Vitality Tracker uses it

Stored as one daily total from the source you chose and charted as a trend; on the activity sheet, each session's figure is labeled with the device that recorded it. It does not enter the TDEE engine, the Vitality Score, Capacity or the Weight Loss Plan.

## How far to trust the number

Estimate, with a measured error of tens of percent. Its direction over weeks on one device is usable; its level is not, and it is not a food budget.

## Method

The maker's model, unpublished; stored as reported.

## Sources

1. Shcherbina A, Mattsson CM, Waggott D, et al. Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. J Pers Med 2017;7:3. [doi:10.3390/jpm7020003](https://doi.org/10.3390/jpm7020003)
2. Vitality Tracker, How Vitality Tracker estimates your energy expenditure, method note v1.0.

## Related

- [Why your watch's calories are not a food budget](https://vitalitytracker.app/knowledge/why-watch-calories-are-not-a-food-budget)
- [The TDEE engine](https://vitalitytracker.app/knowledge/tdee-engine)
- [Activity Units](https://vitalitytracker.app/knowledge/activity-units)
- [Energy sources in a session](https://vitalitytracker.app/knowledge/energy-sources-in-a-session)

Reviewed October 2026 · v1

Source: https://vitalitytracker.app/knowledge/energy-expenditure-device