Free Tools

Health Calculators

Built on validated formulas. Every calculator explains what it's measuring, what it gets right, and where it falls short.

TDEE Calculator

Find your Total Daily Energy Expenditure and Basal Metabolic Rate using the Mifflin-St Jeor formula. Shows calorie targets for every goal from aggressive cut to lean bulk.

Calculate TDEE →

Calculate your Body Mass Index instantly with a visual scale. Includes an honest breakdown of BMI's limitations and what metrics tell a more complete story.

Calculate BMI →

Weight Loss Projection

Enter your current weight, goal, and weekly loss rate. See best-case, expected, and slow-pace goal dates — so you know what to realistically expect.

See Projection →

Macro Calculator

Set your protein, carb, and fat targets from your TDEE and goal. Includes fiber recommendation and per-macro calorie breakdown for cut, maintain, or bulk.

Calculate Macros →

Body Fat % Estimator

Estimate body fat percentage using the U.S. Navy tape-measure method. Shows fat mass, lean mass, and category — no expensive DEXA scan required.

Estimate Body Fat →

How We Build These

Every formula here uses validated research. We document exactly what each calculation does, what its limitations are, and when you should use real data instead of a formula's estimate.

Read: How We Calculate Everything →

Track More Than a Calculator Can

HealthOS calculates TDEE, BMI, VO2 Max, and more from your actual connected data — updating automatically as your weight and activity change.

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