FREE TOOLS
Health Calculators & Tools
Evidence-based health calculators built on peer-reviewed formulas. Get personalized recommendations for nutrition, supplements, sleep, and more.
TDEE & Calorie Calculator
Calculate your Total Daily Energy Expenditure and ideal calorie intake for any goal.
Use Calculator →Macro Calculator
Get your ideal protein, carb, and fat split based on your goals and body type.
Use Calculator →Body Fat % Calculator
Estimate your body fat percentage using the U.S. Navy method with measurements.
Use Calculator →Water Intake Calculator
How much water do you actually need? Personalized by weight, activity, and climate.
Use Calculator →Supplement Dosage Calculator
Evidence-based dosing for Vitamin D, Magnesium, Omega-3, and more by body weight.
Use Calculator →Sleep Cycle Calculator
Find your ideal bedtime or wake time based on 90-minute sleep cycles.
Use Calculator →Caffeine Half-Life Calculator
See when caffeine leaves your system and when to stop drinking coffee for better sleep.
Use Calculator →Inflammation Risk Score
Assess your chronic inflammation risk based on diet, lifestyle, and symptoms.
Use Calculator →Fasting & Autophagy Timer
Track your fast and see when autophagy, fat burning, and growth hormone kick in.
Use Calculator →Biological Age Estimator
Estimate your biological age based on lifestyle factors vs your chronological age.
Use Calculator →Why Use Health Calculators?
Generic health advice fails because every body is different. A 120-pound woman and a 220-pound man have completely different calorie needs, supplement dosages, and hydration requirements. These calculators use peer-reviewed formulas to give you personalized numbers based on your specific body metrics.
Our tools use the same equations used in clinical settings: the Mifflin-St Jeor equation for metabolic rate (validated as the most accurate for healthy adults), the U.S. Navy body fat method (correlates within 3-4% of hydrostatic weighing), and Endocrine Society dosing guidelines for supplements.
Unlike generic "one-size-fits-all" recommendations (drink 8 glasses of water, take 1000 IU of vitamin D), these tools account for your weight, activity level, goals, and lifestyle — producing actionable numbers you can actually use.
How Each Tool Works
TDEE & Calorie Calculator
Your Total Daily Energy Expenditure (TDEE) is the number of calories you burn in a 24-hour period including exercise, digestion, and basic metabolic functions. Our calculator uses the Mifflin-St Jeor equation — validated in 2005 as more accurate than the older Harris-Benedict formula for most adults. It accounts for gender, age, height, weight, and activity level to produce maintenance calories, then adjusts for your specific goal (fat loss at -500 cal/day, lean gain at +300 cal/day).
Calculate your TDEE →Supplement Dosage Calculator
Most supplement labels provide a single "one-size-fits-all" dose regardless of whether you weigh 110 or 250 pounds. Research shows optimal dosing for many nutrients scales with body weight. Our calculator uses guidelines from the Endocrine Society, International Society of Sports Nutrition, and published meta-analyses to compute personalized doses for 8 key supplements: Vitamin D3, Magnesium, Omega-3, Zinc, Vitamin K2, B12, Creatine, and Ashwagandha — including the best forms, timing, and interactions.
Get your personalized doses →Sleep Cycle Calculator
Sleep occurs in 90-minute cycles progressing through light sleep (N1/N2), deep sleep (N3/slow-wave), and REM sleep. Waking during deep sleep causes "sleep inertia" — that groggy, disoriented feeling even after 8+ hours. Our calculator times your alarm to coincide with the end of a complete cycle (the lightest sleep phase), so you wake feeling refreshed. It accounts for the average 15-minute sleep latency (time to fall asleep) and shows options for 4, 5, and 6 full cycles.
Find your ideal bedtime →Caffeine Half-Life Calculator
Caffeine has an average half-life of 5.7 hours — meaning if you drink 200mg at 2pm, you still have 100mg active at 7:45pm and 50mg at 1:30am. Research shows even 50mg at bedtime measurably reduces deep sleep by 20%, even if you fall asleep on time. Our calculator visualizes caffeine decay hour-by-hour and tells you whether your intake timing will affect sleep quality. It also calculates the latest safe time to consume caffeine based on your specific dose and bedtime.
Check your caffeine timing →Fasting & Autophagy Timer
Intermittent fasting triggers a cascade of metabolic changes at different time points: insulin drops at 4 hours, fat oxidation begins at 12 hours, growth hormone surges at 14 hours, autophagy (cellular cleanup) ramps up at 16-24 hours, and deep ketosis establishes at 18+ hours. Our live timer tracks your fast in real-time, showing which milestones you've hit and when the next one arrives. It persists across browser sessions so you won't lose your progress.
Start tracking your fast →Biological Age Estimator
Your chronological age (years since birth) and your biological age (how fast your body is actually aging) can differ by 10-20 years based on lifestyle choices. Research from Blue Zones, the Harvard Study of Adult Development, and epigenetic clock studies shows that exercise, sleep quality, diet, social connections, stress management, and purpose account for 75-80% of how you age — genetics only 20-25%. Our estimator assesses 10 key lifestyle factors and calculates an approximate biological age offset, highlighting which areas to prioritize for maximum longevity benefit.
Estimate your biological age →Frequently Asked Questions
Are these calculators accurate?
Our calculators use formulas from peer-reviewed research and clinical guidelines. The TDEE calculator uses the Mifflin-St Jeor equation (validated ±10% accuracy for most adults). The body fat calculator uses the U.S. Navy method (±3-4% compared to hydrostatic weighing). However, all calculators provide estimates — individual variation based on genetics, medication, and health conditions means results should be used as starting points, not absolute prescriptions.
Do I need to create an account to use these tools?
No. All calculators are 100% free with no registration, no email required, and no data stored on our servers. Calculations happen entirely in your browser. The fasting timer uses your browser's local storage to persist your fast across page reloads — but this data never leaves your device.
How often should I recalculate my TDEE and macros?
Recalculate every 4-6 weeks if you're actively losing or gaining weight, or after any significant change in activity level. As you lose weight, your TDEE decreases (smaller bodies burn fewer calories). As you gain muscle, your BMR increases. Macro ratios may also need adjustment as you approach different phases of your fitness journey.
Should I trust the supplement dosage calculator over my doctor?
No — these are evidence-based starting points based on general population research, not medical advice. Always consult your healthcare provider before starting supplements, especially if you take medications, are pregnant, or have existing health conditions. Blood tests (especially for Vitamin D, iron, and B12) provide far more accurate dosing guidance than any calculator.
What's the difference between BMI and body fat percentage?
BMI (Body Mass Index) only considers height and weight — a muscular athlete and an obese person of the same height/weight have identical BMIs despite completely different body compositions. Body fat percentage directly measures how much of your mass is adipose tissue vs lean mass (muscle, bone, organs). Our body fat calculator uses the U.S. Navy circumference method, which is more informative than BMI for most people.
Is the biological age estimator scientifically valid?
Our estimator uses lifestyle factors that are strongly correlated with biological aging in published research (exercise, sleep, diet, stress, social connections, etc.). However, it provides an approximation, not a clinical measurement. True biological age testing requires DNA methylation analysis (epigenetic clocks like Horvath's or GrimAge) or comprehensive blood biomarker panels. Our tool helps identify which modifiable factors to prioritize.
Continue Learning
🧠 Health Quizzes
Test your knowledge with 30 evidence-based health quizzes covering nutrition, supplements, longevity, and more.
💊 Supplement Guides
In-depth guides on specific supplements with dosing, interactions, and product recommendations.
🦠 Gut Health
Everything about the microbiome: probiotics, prebiotics, gut-brain axis, and digestive optimization.
⏳ Longevity Science
Anti-aging research, Blue Zones, NAD+, telomeres, and evidence-based strategies for a longer healthspan.