The Apple Watch and Resting Calories
I’ve highlighted how the Apple Watch isn’t very accurate as a fitness tracker, and I’ve shown that my Apple Watch’s heart rate sensor doesn’t work correctly, which is leading Apple to exchange it.
But one thing I find surprising is the way the Apple Watch – or, more correctly, the Activity app on your iPhone – calculates resting calories. This is another term for basal metabolic rate, or BMR, the amount of energy your body expends just to keep you alive. If you did absolutely nothing during a day, other than sleep, your body would still burn a certain number of calories. In fact, your active calories only represent a small part of the amount of energy you use.
Like many such measurements that are difficult to measure, the BMR varies according to the way it’s calculated. But one such calculator tell me that may BMR is 2008 calories. Another one, at myFitnessPal, tells me my BRM is 1894 calories.
Not Apple. According to the Activity app, my resting calories for the full day yesterday was 3184, or 50% more than a BMR calculator. As such, the Activity app tells me that I burned 3829 calories yesterday, with 645 of these being active calories. Yesterday, I took two brisk walks: one on my treadmill, for 30 minutes, which counted as 178 calories, and one outdoors, for about 20 minutes, which clocked 83 calories.
It’s interesting that the 20-minute outdoor walk only counted for about half as much as the 30-minute indoor walk, which measured calories based on my heart rate, and, presumably, the frequency of my steps.
No matter how you slice it, these numbers are wrong. I’ll give Apple a pass on the active calories; there’s no way to get those numbers down precisely. But the BMR, or resting calories? I’ve entered my data in the health app – age, height, weight and sex – so, unless online calculators are way off the mark, Apple has some tweaking to do.
What’s also surprising is that this number isn’t the same every day; it ranges from 3172 to 3195. This is a fixed number, that has nothing to do with my activity. There’s not a big difference between the top and bottom of the scale, but they should be the same every day. Only the active calories should change. (Update: this is because my weight changes slightly every day; I use a wireless scale which syncs its data to HealthKit.)
And this is particularly worrisome. This number is based on a very simple calculation, and isn’t skewed by the way you move your arms, or your stride when you walk. It’s the one number that they should get right.




There’s gotta be something wrong with your watch. I’ve check my activity app and my Resting calories are always 2335 for every day.
But it’s not the watch that calculates resting calories, it’s the Activity app. So it can’t be a problem with the watch itself. Many other users see this problem too.
Seems to me that the resting calories should vary each day since you would subtract the amount of time active calories are counted. If there is a calculated max of 2,400 per 24 hours (100/hr) and you were active for 1 hour, I would expect the resting calories to be 2,300 that day, not 2,400…
No, active calories are counted in addition to resting calories when you’re active. You can see this in the Activity app on the iPhone if you’ve recorded any workouts; the app shows the amount of active calories, and resting calories, for the period of the workout.
I know this is an old thread, but I am exploring how the Apple Watch works relative to health. I don’t think that resting calories has the same definition as BMR. Resting calories represent anything you are doing that is not exercise. The app literally records your heart rate every single minute… One minute, sitting motionless in a chair, you will burn .2 calories. If you lean forward in your chair the next minute, and your heart rate goes up a tad, you might burn .7 calories. The Health App adds up all of these minute-by-minute caloric expenditures during the day to arrive at both your active and resting calories.
No, that’s incorrect. It only checks your heartbeat every 10 minutes, and only if you’re not moving at the time. The exception is if you are doing a workout, during which it checks your heart rate continuously.
Kirk, go into your Health app, not the Activity app. Health Data > Fitness > Resting Energy > Show All Data. You can see the data points being added. Click into them. The total of those daily data points should match your Activity app. total. In my case, there’s a new data point from my watch almost every minute of the day. When I’m not wearing the watch, the data points entered appear to be an average. This would explain the daily variance. I believe you’re assuming a static daily formula based on fixed measurements rather than considering fluctuating input from the Watch sensor by minute. Btw, my high and low fluctuates in line with yours and my Apple Resting Energy is lower than in the BMR apps you linked to. Also has nothing to do with your wifi scale, I don’t use one, or manually updating your weight daily. I don’t do that either. Also, I don’t see where Apple has ever claimed this to be a standard BMR calculation.
If you look at the data, you’ll see it looks like random numbers, and you can see that it’s not added every second. The precise time it’s added isn’t specified, so sometimes you don’t have an entry for a given second. When you look at the total by day, it’s stable; the only variant would be your weight.
I have the same problem, yesterday my resting calories were 1808 and today it was 1705.
But I just realized that the time you physically take off the watch can vary the resting calories as well. For example, if I took my watch off at midnight and it was 1808, yet the next day I took my watch off at 10pm, then my BMR would be lower because I did not have it on for the remaining two hours of the day. Theoretically, they should just keep it the same every day and show the same BMR at the end of the day regardless of what time the watch was physically removed, however, they may not do this.
If I look in the Activity app at days where I only wore the watch for a few hours, my resting calories are roughly the same. They shouldn’t change from day to day; the number is for the full day, not the time you wear the watch.
Mine varies slightly and I assumed it was due to my weight being updated by my wireless scale.
Hmm, good point. I’ll have to check that; I have a wireless scale too.
Exactly, the only variant in calculating the BMR formula is your day-to-day weight. My resting calories change everyday because I update my weight everyday in the Health app.
My big wish is for Apple to add body fat percentage into the resting calorie formula because that can alter it significantly. I use one of the handheld devices to measure my body fat %. A person’s metabolism ultimately determines most of your resting calories, and that’s all genetics, so that just goes to show this is all just a guessing game anyways.
You’re not correct to say that resting calories are always the same. For instance, if you do 20 mins of high intensity interval training, you’ll see a spike in Resting Energy Expenditure (REE) for up to 24 hours.
I don’t do high intensity interval training. I get your point, but the numbers are just wrong.
This is a known bug with the activity app.
I’ve had it confirmed to me by Apple support.
My suspicion is they’re using lb/in in a formula that expects kg/cm
I hadn’t thought of that.
Any news on this topic?
I’ve bought my apple watch this week and I’m unhappy to see how it overestimate my resting calories and it underestimate my active calories :-(
Resting calories are a generality in apps. Resting calories vary with composition. Fat burns burns less calories than lean tissue, lean tissue more than fat tissue.
Resting calories of people with identical weight would be greater for the person with less body fat.
Does anyone know how to remove the calorie counter from the watch? I use the other trackers – but don’t need/don’t want the calorie counter. I don’t want to lower or raise the number of calories (I know how to manipulate the goals). I’d like to delete the calories and save some battery. I’ve burned a lot of calories trying to figure this out on my own. Appreciate your help.
You can’t. There is nothing customisable about the tracking.
Is it possible that the “resting calories” counts all the time when you’re not literally tracking a workout? So for instance, one day I’m walking around a lot at work (in a hospital) and I lift a bunch of things and go up and down a few flights of stairs. Then I go home and do my normal 25 minute workout. Another day I don’t move as much at work or I’m in the car for a longer stretch than usual. Then I go home and do the same workout.
The app automatically counts some moving time as exercise but we don’t know that formula either, so perhaps the “resting” calories isn’t exactly BMR but more based on the “non-workout” activity we did on a given day?
I’m still trying to figure this out after a year. I have a calorie goal of 900 (that I only hit when I am active at work all day AND exercise) and I don’t track my calories, but if I did, I’m not exactly sure how the ~900 really counts towards my daily intake and output.
Idk, maybe I’m dumb.
Let me know what you think.
No, as I explain, resting calories are what your body burns to keep you alive. It’s everything other than movement. And, anyway, counting calories is a bit useless, since a) calorie counts for foods are just estimates, and b) we don’t necessarily get all the calories in certain foods. It’s a rough estimate at best, but one that scientists increasingly realize is way off the mark.
I disagree. Counting calories isn’t useless. Yes, it is near impossible to be completely accurate, but having a general idea of the calories you are putting in your body vs. the calories out can be very beneficial. I’ve been counting calories off and on for over a decade. It is the only way I have been able to lose weight and keep it off.