Open Calculators
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Biometric Modeling & Energy Balance

Health & Fitness Calculators

Ground your nutrition, weight management, and athletic conditioning in verified physiological science. All calculations evaluate locally in your browser with zero data transmission and absolute medical privacy.

Suite 1

Core Body Metrics & Composition

WHO Spectrum

BMI Calculator

WHO standard classifications, Prime BMI, Ponderal index, and healthy target weight ranges.

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U.S. Navy Method

Body Fat Calculator

Circumference tape method, lean mass vs. fat mass, military readiness, and target fat goal weight.

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Devine & Hamwi

Ideal Body Weight (IBW)

Multi-formula clinical baseline weights, wrist frame adjustment, and Adjusted Body Weight (ABW).

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Hydration Science

Daily Water Intake

Evidence-based fluid needs tailored to body weight, exercise sweat rate, climate, and urine color.

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Suite 2

Metabolism & Nutrition (The Energy Balance Funnel)

Mifflin-St Jeor

Calorie Deficit & TDEE

Compute Total Daily Energy Expenditure (TDEE), BMR, sustainable deficit tiers, and goal dates.

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Flexible Dieting

Macro Calculator (IIFYM)

Convert target calories into grams of protein, carbs, and fat with locked sliders and meal schedules.

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Clinical Gold Standard

BMR Calculator (Harris vs. Mifflin)

Side-by-side formula benchmark comparing Mifflin-St Jeor, Revised Harris-Benedict, and Katch-McArdle.

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Suite 3

Athletic Performance & Conditioning

Epley & Brzycki

One-Rep Max (1RM) Calculator

Estimate maximum barbell strength from submaximal reps, generate percentage tables, and plate loadouts.

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Karvonen & Tanaka

Target Heart Rate & Zones

Calculate beats-per-minute ranges for Zone 2 fat oxidation, tempo training, and VO2 max intervals.

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Pete Riegel Model

Running Pace & Race Predictor

Pacing splits per mile/km, marathon finish time predictions, and treadmill 1% incline speed compensation.

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Suite 4

Women's & Family Health

ACOG Obstetrics

Pregnancy Due Date & Gestational Age

Calculate estimated delivery dates via Naegele's rule, track 40-week gestational age, compare weekly fetal fruit sizes, and plan prenatal clinical testing.

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Luteal Subtraction

Ovulation & Fertile Window

Pinpoint conception windows, peak fertility days, and 6-cycle calendar projections with luteal phase adjustments.

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Physiological Rigor & Medical Governance

The Interconnected Calculation Chain

Human metabolism operates as an integrated biological system. Rather than calculating in silos, our tools pass user parameters seamlessly across the calculation chain: screening with BMI, measuring tissue distribution via U.S. Navy circumference body fat models, establishing metabolic burn floors with Mifflin-St Jeor and Katch-McArdle equations, and allocating optimal protein, carbohydrate, and fat targets for muscular preservation.

Medical Disclaimer & Clinical Safety

All tools, equations, and guidelines provided on Open Calculators are intended solely for educational, informational, and personal planning purposes. They do not constitute formal medical diagnosis, individualized clinical prescription, or obstetrical advice. Always consult a licensed physician, registered dietitian, or sports medicine professional before initiating aggressive caloric deficits or intensive exercise routines.