Calories burned discrepancy

I’m new to Zwift.
I’ve been using Polar H10 heart rate monitor (connected to Polar V800)
after 50 minutes ride Zwift shows 440 calories burnt, whereas Polar is showing 700.
Both platforms have the same statistics set up (age, weight, height etc).
can anyone explain the huge discrepancy?


activity intensity is a factor too… what does this calculator says?

read this one too :wink:

thanks for your response. Based on the calculator in your link Polar is spot on and Zwift is way off.

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Zwift uses power (wattage) to calculate calories burned, not heart rate.

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My guess would be that zwift will be closer as it uses power (assuming you have a power meter or smart trainer).

if using calorie estimates for weight loss always pick the lowest. Whichever you use will always have assumptions built into the calculation somewhere and so none will be very accurate.

Do calories really matter? Why is this the metric that people track? We know it is, at best, a complete guess in the first place. Calories in calories out (CICO) has been proven to be an unsustainable and extremely difficult way to lose weight (I assume that is why you are tracking calories, why else would you?). Dr. Jason Fung explains the process here.


having read that he still says that you need to consume fewer calories than you burn though - just be clever about which calories you consume and when.

If you zwift with a power meter, zwift is correct and polar is way wrong

Calories can’t be tracked accurate just based on hr


it can’t be with a power meter either, it is far more accurate though. It has to assume how efficient your body is and extra calories are burned depending on how much you move around on the bike/how hot you are etc

but, yes, power meters are a much better indicator


I know I’m late to the party. I’m using the Polar OH-1+ (forearm/bicep heart rate monitor). Map my ride and Polar indicate around the same amount of calories burned when compared to Zwift. Zwift is way off. I weigh myself after my cycling workouts. I can assure you Polar or Map My Ride estimates are probably more accurate based on the article below. I don’t know why Zwift doesn’t give you the option of using data from Polar. Zwifts algorithm for calories is trash.

The researchers evaluated seven fitness-tracking devices with the help of a small group of 60 volunteers and found that six of the devices were accurate for heart rate to within 5 percent. None of the devices were from the Polar brand, but the findings are still helpful for understanding that even when heart rate accuracy was good, the accuracy of measuring energy expenditure was not: The most accurate device was off by 27 percent, and the least accurate was off by a staggering 93 percent.

But with Polar heart rate monitors so often functioning as the gold standard for measuring heart rate, is it possible that they fare better?

The answer is a mixed bag, depending on which model is evaluated and the activity that they were used to gauge. For example, in a study published in a March 2010 issue of the *[British Journal of Sports Medicine], researchers found that the Polar Activity Watch 200 fell within the accepted 10 percent error threshold of calorie estimates — when used while hiking. They didn’t evaluate the AW200 during other activities.

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very late to this forum but came across this and figured I would answer nonetheless.
Calories are important as a estimate in energy expenditure. If zwift is only using watts as a source, it might not be accurate for an individual who has a phenomenal Vo2max compared to someone who doesn’t (and other factors as well)
For sure there are those who use it for weight loss but there are also those who use it to tailor the calorie intake on long endurance rides. Consuming calories, often referred to as the 4th discipline in ironman, is extremely important when performing at high levels.
Theoretically, your HR zone will indicated what type of energy system you are using (aerobic vs anaerobic) this relationship can also help indicate what type of energy/ calorie we should consume (long and slow= no need for fast metabolizing sugars IN HIGH amounts/ , hard and fast = sugars please).
When it comes to calories there is most definitely a role.
watts, weight, height, gender, and hear rate are all important when looking at weight loss, endurance building, strength training, hormones, and an overall healthy lifestyle.
hope this somewhat clarifies why Calories can be seen as important.


Dear Udi - and anyone else who’s interested. Let’s start with definitions.

A calorie, or kilocalorie, is a unit of some form of energy (the energy required to increase the kinetic energy of the water molecules in a volume of water). A joule, or kilojoule, is also a unit. Specifically, it’s a unit of work. A joule, roughly, is the amount of work done by a force to move an object through a given distance. And, so what?

Well. When you’re sitting around doing nothing, you’re not moving anything, so the work, in joules, is zero. Because zwift only calculates ‘pizza slices’ based on work done, you don’t have to subtract a ‘baseline’ amount of energy from your overall calculated energy output at the end of your ride, because your ‘baseline metabolic work’, is zero. This is basic physics.

Heartrate calculations, on the other hand, require a subtraction of a baseline energy amount. That’s because your heart is always pumping, in order to keep cells respiring. So, any heartrate increase above that baseline for a given period of time, is correlated with the amount of energy (‘calories’) expended for that time. But: you’ll need to subtract the amount of energy that would’ve been expended just for keeping them cells of yours alive!

As far as the energy listed on food labels: obviously it’s an estimate. But it’s the only estimate consumers have. So it’s a good place to start. And measuring calories in, calories out, if done systematically, is the only sure-fire method to have a reasonable measure of the ‘energy budget’ of one’s body. Exceptions would be if you had thyroid dysfunction, for instance.

Triglycerides require beta oxidation in order to be used for cells to make proteins etc. So that’s why fat is not a direct source of energy. Glucose is the only immediate source, and protein, fat, and alcohol, must all be converted into suitable-length carbon chains.

Eating fat won’t help you change your body composition, regardless of leptin and grhelin and satiety, because you’ll be forced to replace foods with 4kcal per gram, with foods that have 9kcal per gram. That is: you’ll forego lesser energy-dense foods for more energy-dense ones. So, even if you are sated more often, your less frequent meals will rely on more energy-dense items anyway, so it’ll require even more calculation to find out if there’s some advantage. (This last point is a priori true. No degree in nutrition needed. Until 9=4, substituting lipids for carbs won’t work. Which is why counting calories is the sensible strategy).

Is changing body composition in a favorable direction difficult? Yes. Can you measure things to gain a greater grasp of where to change things in order to aid favorable changes? Yes. Is it a hassle? Yes. But so is pulling off the highway to fill your petrol tank when the gauge shows an empty tank. Guesswork leads to disappointment. Calorie counting is guesswork, but it’s systematic guesswork, and can be a reliable, replicable and informative method to achieve things.

So if i sit around doing nothing i need no energy? really?

You’re not doing work. That’s what i said.

I’m keeping myself alive - that requires energy.