Your Phone's Calorie Burn Number Is a Guess
Your phone counts steps well, but its active-calorie number is only a rough estimate from a formula. Burnie lets you fix that number with a manual override when you know better.
Your phone says you burned 320 active calories today. That number looks exact and final. But it is really a smart guess, not a true measurement. Your phone is great at counting steps. It is only okay at turning those steps into calories. Here is what is going on, and the simple fix Burnie gives you.
My phone's active-calorie number is exact, so I can eat those calories back.
mostly falseMostly false. Your phone's calorie burn is an estimate from a formula, not a real measurement. A famous Stanford study of motion-based fitness devices found the best device was off by an average of 27 percent on calories, and the worst was off by more than 50 percent. So treat the number as a rough guide, not a permission slip to eat more.
Steps are counted. Calories are guessed.
Your phone has a tiny motion sensor that feels each step you take. That part is direct, like counting coins. But calories are not sensed. The phone turns your step count plus your body weight into a calorie number using a formula. Scientists call this an indirect estimate. One Stanford researcher put it plainly: heart rate is measured directly, whereas energy expenditure must be measured indirectly through proxy calculations. So the step count on your phone is fairly trustworthy, but the calorie number on top of it is a guess that can be way off for your body.
What your phone gets right and what it gets wrong
What to do about the error
The bottom line
Trust your phone's step count as a rough guide. Treat its calorie burn as a guess — and override it in Burnie with PUT /api/summary/daily/active-calories when you have a better number. Put your real effort into logging food before you eat. That is the side you control.