Active Energy on Apple Watch: What Your Move Calories Mean

For many people, the red Move ring is the number they check most often, and it is also one of the easiest to misread. Active energy is an estimate, and it covers only part of the energy you use in a day. Here is what it describes, how Apple Watch arrives at it, and where My Bio Age uses it.

Active energy versus total energy

Apple's HealthKit documentation defines active energy as the energy burned through physical activity and exercise, excluding the resting energy burned over the same period. Resting energy, also called basal energy, is what your body uses to function at rest. Apple's technical paper on heart rate and calorimetry notes that Apple Watch reports both, and that together they make up your total calories.

So your Move calories are not everything you burned that day, only the extra attributed to moving. Both figures are estimates, better for comparing your own weeks than for precise accounting.

How Apple Watch estimates it

Apple's daily activity guide says the red Move ring shows the active calories you have burned. The technical paper explains that, through the day, the watch relies mainly on motion data and an activity classifier that recognises what you are doing. During a workout it adds heart rate and, outdoors, GPS, which Apple says makes workout estimates more robust. It then uses your weight and the time spent at each level of effort to convert the result into calories. To make the estimate more dependable:

• Keep your Health profile up to date. Apple uses weight, height, age and sex in its calorie estimates, so an out-of-date weight shifts every total.
• Let the watch calibrate. Apple's calibration guide explains that outdoor walks and runs with good GPS help the watch learn your stride and fitness, improving its calorie, distance and pace estimates.

How My Bio Age totals your day

My Bio Age reads active energy from Apple Health in kilocalories and adds each day's records into one daily total. Other apps and devices can save active energy to Health too, so your watch and a separate workout app may both record the same run.

Rather than adding everything, My Bio Age lines the records up by time. An overlapping stretch is counted once, and only a proportional share of a record that runs beyond it is added, so a second tracker should not double your day. Because of this, and because a record that runs past midnight counts towards the day it ends, the daily total in My Bio Age can differ from your Move ring or the Health app, especially on days with more than one source.

For each complete Monday-to-Sunday week, the daily totals are averaged into one of the weighted inputs to the MyBioAge Index™. The app compares that average with reference values for your age and sex, and more activity counts in your favour, up to a limit. Days with no records are left out of the average, and a week with fewer than five days of records counts with less confidence. If a whole week has no records, the app reuses your most recent daily total from the week before, at reduced confidence. A day when you wore the watch for only a few hours still counts at a low total, so steady wear gives a fairer picture.

Where else active energy appears

Active energy also supplies the activity signal for three daily scores, each with its own time window.

• Training Load. The ratio compares your average daily active energy over the last 7 days with the last 28; about 1.0× means your usual level. Days without records count as zero, so a few days off the watch can look like a lighter week. An Activity Pattern signal looks at how regularly you have been active over 14 days, and the score also needs recent HRV. Training Load's weekly average is also one of the MyBioAge Index™ inputs, and a ratio close to your usual level scores best. Our guide to the acute:chronic ratio explains the bands.
• Stress Resilience. Its training-stress component makes a similar 7-day versus 28-day comparison and needs about two weeks of records from the past four. HRV is still required for any Stress Resilience score.
• Circadian Alignment. A smaller component, Activity Timing vs Sleep, makes up about 15% of the score; sleep timing makes up most of the Circadian Alignment score.

Calories are not the target

Public health guidelines describe activity in minutes and intensity, not calories. The CDC recommends that adults get at least 150 minutes a week of moderate-intensity activity, such as brisk walking, or 75 minutes of vigorous activity, or an equivalent mix, plus muscle-strengthening activity on at least two days. The 2020 WHO guidelines give weekly ranges of 150 to 300 moderate or 75 to 150 vigorous minutes, and the WHO fact sheet stresses that any amount of activity is better than none. My Bio Age's Active Energy detail view also gives its guide in minutes.

• Don't compare totals with friends. Because weight feeds into the conversion, a larger person can burn more energy on the same walk. A bigger number on someone else's wrist doesn't mean they moved more.
• Count everyday movement. WHO counts walking to get places, work and household tasks as physical activity, and the watch estimates active energy outside workouts too.
• Build up steadily. A sudden jump in activity pushes your Training Load ratio well above your usual level, while a gradual increase keeps it closer to your normal range.

Putting it together

Read active energy as a steady record of how much you move, compared with your own recent weeks. To see it beside your recovery, read using the Recovery dashboard alongside your Activity rings. For a routine built around movement, see our daily habits guide. Our Methods & Sources page explains the approach in more depth.

To see how your own movement compares across weeks, download My Bio Age free on the App Store and connect the Apple Health data you choose. The iPhone app is completely free, with no in-app purchases, subscription or account required. Your health data stays on your iPhone, where active energy, Training Load and your weekly Index are calculated.

My Bio Age provides general wellness information, not medical advice. If you have a heart condition or a long-term illness, the NHLBI suggests asking your doctor which activities are safe and how to build up. If you feel chest pain or dizziness while active, stop and seek medical advice. The NHS says to call 999, the UK emergency number, for chest pain that comes on suddenly and doesn't go away, or that comes with sweating, sickness, light-headedness or shortness of breath.