Severe Underestimation of Calories Burned in iPhone Fitness App (Without Apple Watch)

My recent experience highlights a potential flaw in how the app calculates energy expenditure based on walking activity.

My profile and experience:

• Male, 39 years old, 90kg, 6 feet tall (all details double-checked in the Health app)

• Activity: Walked 2.14 km (3,576 steps), as correctly recorded by the Fitness app

• Calories shown as burned: only 21 KCAL

Key points:

• The iPhone accurately detected the number of steps and distance, proving the sensors are functioning properly.

• All my personal input data (age, height, weight, sex) are absolutely correct.

• Scientific calculators and widely accepted fitness formulas (including MET-based calculations) indicate that I should have burned approximately 130–170 KCAL for this activity and profile—not merely 21 KCAL.

• The undercount is not trivial: the result is over 6 times lower than any credible calculation for walking this distance at my weight, with every input otherwise correct.

Why this is a problem:

• The Apple Fitness app’s estimate is so far outside validated norms that it cannot be trusted for any health or fitness tracking purposes.

• With all data inputs and sensors functioning accurately, the problem can only be in the proprietary formula Apple is applying to convert steps/distance/weight/height into calories.

• This seriously misleads users—particularly those who rely on accurate calorie counts for weight management, fitness, or medical purposes.

Request:

• Please review and correct the calorie calculation algorithm in the iPhone Fitness app for users not using the Apple Watch.

• At minimum, ensure that the formula aligns far more closely with standardized, science-backed methods used throughout the fitness industry.

• Transparency about the formula and calculation method would be greatly appreciated, or—ideally—the option to select a formula based on published research for more accurate tracking.

The Fitness app’s current approach underestimates my calorie burn by a vast margin, despite all correct sensory and user data. Until this is addressed, users are being misinformed about their activity levels and energy expenditure, which undermines the usefulness and credibility of the Apple Fitness ecosystem for anyone not using an Apple Watch.

Thank you for your attention to this matter. I—and many others—would greatly appreciate a resolution.