In short: the source can change from day to day, missing days stay unavailable, and no source is an exact measurement of an individual's metabolism.
What the number means
The result is an estimate of total energy expenditure across a day, expressed in kilocalories (kcal). It is not a direct measurement of metabolism and is not a promise of how many calories a particular person actually used.
The fallback starts with estimated resting energy expenditure (REE), then scales it with an activity factor. You may also see the broader term total daily energy expenditure (TDEE) used for this kind of estimate.
Source order
For each day, KnowsYou uses the following order:
- A finite, non-negative WHOOP-reported daily energy estimate, when one exists.
- The profile-based fallback, when all required profile inputs are available.
- “Unavailable” when neither source can produce a value. Missing data is not silently changed to zero.
WHOOP and other consumer wearables infer energy expenditure from sensor data and models. Accuracy can vary by device, person and activity.
The fallback formula
KnowsYou uses the Mifflin–St Jeor predictive equation for adults. Weight is in kilograms, height in centimeters and age in years.
REE = 10 × weight + 6.25 × height − 5 × age + 5
REE = 10 × weight + 6.25 × height − 5 × age − 161
Estimated daily expenditure = estimated REE × activity factor
The published equation uses two sex-based constants. That binary structure is a limitation of the method, not a complete model of an individual’s physiology.
For a given date, the app uses the most recent recorded weight on or before that date. It does not apply a later weight retroactively. If no eligible weight record exists, the fallback is unavailable.
Activity factors
The selected lifestyle category supplies the multiplier below. These factors are heuristics and are not part of the original Mifflin–St Jeor equation. A self-selected category can add substantial uncertainty.
| Level | Product description | Factor |
|---|---|---|
| Sedentary | Mostly seated, with little intentional exercise | 1.2 |
| Lightly active | Light exercise or an active day 1–3 times a week | 1.375 |
| Moderately active | Moderate exercise or an active day 3–5 times a week | 1.55 |
| Very active | Hard exercise or a highly active day most days | 1.725 |
Worked example
Consider a hypothetical 35-year-old using the female equation option, at 70 kg and 165 cm, with “moderately active” selected.
10 × 70 + 6.25 × 165 − 5 × 35 − 161 = 1,395.25 kcal/day
1,395.25 × 1.55 = 2,162.64 kcal/day
The app rounds this to 2,163 kcal/day. It remains a profile-based estimate, not a personalized measurement or intake target.
How energy balance is shown
KnowsYou uses one sign convention throughout the app:
logged intake − estimated expenditure
- A negative value represents an estimated deficit.
- Zero represents estimated maintenance.
- A positive value represents an estimated surplus.
Both sides can be uncertain: meal intake may be incomplete or approximate, and expenditure is estimated. The difference can compound those errors.
Missing data and period averages
A period average includes only days with the required numeric values. For intake, a day counts as covered once at least one logged item has a calorie value; this does not prove the whole day was logged. Days with no calorie values are excluded rather than changed to zero.
- Energy-burn averages use days that have either a WHOOP-reported estimate or a profile-based estimate.
- Energy-balance averages use only days that have both intake and expenditure values.
- Coverage shows days with any logged calorie values and days with none. Logged items without calories are flagged separately, but omitted meals on an otherwise covered day cannot be detected.
Inputs and limitations
The fallback requires date of birth, one of the equation’s two sex options, height, weight and an activity level. Current input validation accepts adults aged 18–120, heights of 100–250 cm and weights of 20–500 kg. Those software bounds are not a statement that the equation is equally validated across those ranges.
- The original equation was developed from 498 adults aged 19–78; performance for an individual can differ materially.
- Body composition, pregnancy, breastfeeding, eating-disorder history, illness, medication, metabolic adaptation and other factors are not represented directly.
- Activity categories compress variable daily behavior into one broad multiplier.
- Wearables and the profile fallback should be used for general trends, not clinical decisions or exact food prescriptions.
The fallback is not calculated for people under 18. Do not use this estimate to manage a medical condition, dose medication or make treatment changes. Pregnancy, breastfeeding, eating-disorder history and other individual circumstances require qualified, individualized guidance.
References
- Mifflin MD et al. (1990)Original predictive resting-energy equation study
- Frankenfield D et al. (2005)Review of predictive energy equations in adults
- O’Driscoll R et al. (2020)Systematic review of wearable energy-expenditure validity
Published · Method version 1.0 · Last changed
1.0 · July 22, 2026 — Initial publication of the equation, source order, activity factors, period rules and limitations used by the app.