Methodology & Sources

⚖️ BMI Calculator

Formula: BMI = weight (kg) / height (m)²

Classification: Based on World Health Organization (WHO) standards:

• Underweight: BMI < 18.5
• Normal weight: BMI 18.5 - 24.9
• Overweight: BMI 25.0 - 29.9
• Obese: BMI ≥ 30.0

Limitations: BMI does not account for muscle mass, bone density, age, sex, or ethnicity. Athletes and muscular individuals may have high BMI despite low body fat.

Source: World Health Organization (WHO) BMI classification standards

☕ Caffeine Half-Life Calculator

Formula: Exponential decay model based on first-order pharmacokinetics

Half-life: Average caffeine half-life is 5 hours in healthy adults (range: 3-7 hours)

Calculations:

• Amount remaining = Initial dose × 0.5^(time elapsed / half-life)
• Percentage remaining = (Amount remaining / Initial dose) × 100

Limitations: Caffeine metabolism varies based on genetics (CYP1A2 enzyme), smoking status, pregnancy, liver function, and medications. Individual half-lives can range from 1.5 to 9.5 hours.

Key Sources: Nehlig (2018) in Frontiers in Psychiatry; Blanchard & Sawers (1983) in Clinical Pharmacokinetics

🍷 Alcohol Sleep Impact Calculator

Methodology: Estimates sleep debt based on alcohol's effects on REM sleep and sleep architecture

Key Effects:

• REM sleep suppression: ~10-20% reduction per drink
• Sleep fragmentation: Increased awakenings in second half of night
• Reduced sleep quality: Despite faster sleep onset

Limitations: Individual responses vary based on tolerance, genetics, body composition, and timing of consumption. The calculator provides general estimates, not personalized predictions.

Key Sources: Ebrahim et al. (2013) in Alcoholism: Clinical and Experimental Research; Roehrs & Roth (2001) in Alcohol Research & Health

⚡ Circadian Rhythm Calculator

Methodology: Predicts energy peaks and dips based on sleep/wake schedule and circadian biology

Key Principles:

• Circadian alertness peaks 2-3 hours after waking and 6-8 hours after waking
• Post-lunch dip occurs 7-9 hours after waking
• Evening alertness decline begins 2-3 hours before habitual bedtime
• Lowest alertness occurs 2-4 AM (biological night)

Limitations: Does not account for individual chronotype (morning lark vs. night owl), sleep debt, light exposure, or caffeine consumption. Predictions are based on population averages.

Key Sources: Refinetti (2016) Circadian Physiology; Monk et al. (1997) in Chronobiology International

🚭 Smoking Cessation ROI Calculator

Methodology: Calculates financial savings and health improvements after quitting smoking

Financial Calculation: Daily cigarettes × Pack size × Pack price × Time period

Health Timeline: Based on American Cancer Society guidelines:

• 20 minutes: Heart rate and blood pressure normalize
• 12 hours: Carbon monoxide levels return to normal
• 2-12 weeks: Circulation improves, lung function increases
• 1-9 months: Coughing and shortness of breath decrease
• 1 year: Heart disease risk drops by 50%
• 5 years: Stroke risk equals that of non-smokers
• 10 years: Lung cancer risk drops by 50%

Limitations: Health benefits vary by individual factors including age, smoking history, and overall health. Financial savings don't account for healthcare costs or indirect expenses.

Key Sources: American Cancer Society smoking cessation guidelines; U.S. Surgeon General reports on smoking and health

😴 Sleep Apnea Risk Assessment

Methodology: Risk assessment based on validated clinical screening tools

Risk Factors Evaluated:

• Loud snoring
• Observed breathing pauses during sleep
• Excessive daytime sleepiness
• High blood pressure
• BMI over 35
• Age over 50
• Neck circumference (males >17", females >16")
• Male gender

Limitations: This is a screening tool, not a diagnostic test. Only a sleep study (polysomnography) can definitively diagnose sleep apnea. High-risk results warrant consultation with a sleep specialist.

Key Sources: Based on STOP-BANG questionnaire and American Academy of Sleep Medicine guidelines

💤 Sleep Debt Calculator

Methodology: Calculates cumulative sleep deficit based on recommended sleep duration minus actual sleep

Formula: Sleep Debt = (Recommended Sleep − Actual Sleep) × Days

Recommendations by Age:

• Adults (18-64): 7-9 hours per night
• Older adults (65+): 7-8 hours per night
• Teenagers (14-17): 8-10 hours per night

Limitations: Individual sleep needs vary. Some people function well on less sleep while others need more. Quality of sleep matters as much as quantity.

Key Sources: National Sleep Foundation sleep duration recommendations; Walker (2017) Why We Sleep

😴 Nap Optimizer

Methodology: Recommends nap duration and timing based on sleep cycle architecture and circadian rhythm

Nap Types:

• Power nap (10-20 min): Light sleep stages, quick refresh
• Recovery nap (60 min): Includes slow-wave sleep for memory
• Full cycle (90 min): Complete sleep cycle, avoids inertia

Limitations: Optimal nap timing depends on individual chronotype and sleep pressure. Napping too late can interfere with nighttime sleep.

Key Sources: Milner & Cote (2009) in Sleep Medicine Reviews; Brooks & Lack (2006) in Sleep

✈️ Jet Lag Recovery Calculator

Methodology: Calculates adaptation schedule based on time zone shift and circadian phase response curves

Recovery Rate: Approximately 1 day per time zone crossed (faster for westward travel)

Light Exposure Timing:

• Eastward travel: Morning light exposure advances circadian rhythm
• Westward travel: Evening light exposure delays circadian rhythm
• Avoid light at opposite times to prevent counter-adjustment

Limitations: Individual adaptation rates vary. Age, direction of travel, and prior sleep debt affect recovery time.

Key Sources: Eastman & Burgess (2009) in Sleep Medicine Clinics; Waterhouse et al. (2007) in The Lancet

🔥 TDEE Calculator

Formula: Mifflin-St Jeor equation for Basal Metabolic Rate (BMR)

• Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
• Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Activity Multipliers:

• Sedentary: BMR × 1.2
• Lightly active: BMR × 1.375
• Moderately active: BMR × 1.55
• Very active: BMR × 1.725
• Extremely active: BMR × 1.9

Limitations: Equations provide estimates; actual needs vary based on body composition, genetics, and metabolic adaptation.

Key Sources: Mifflin et al. (1990) in American Journal of Clinical Nutrition

🥗 Macronutrient Calculator

Methodology: Calculates protein, carbohydrate, and fat targets based on calorie goals and diet type

Caloric Values:

• Protein: 4 calories per gram
• Carbohydrates: 4 calories per gram
• Fat: 9 calories per gram

Preset Ratios: Based on common dietary approaches (balanced, low-carb, high-protein, keto, etc.)

Limitations: Optimal macros depend on individual goals, activity type, and metabolic health. These are starting points for experimentation.

Key Sources: Dietary Guidelines for Americans; Position statements from Academy of Nutrition and Dietetics

💧 Water Intake Calculator

Base Formula: 30-35 mL per kg of body weight, adjusted for activity and climate

Adjustments:

• Exercise: +500-1000 mL per hour of activity
• Hot climate: +500-750 mL per day
• Caffeine: Additional water to offset diuretic effect

Limitations: Individual needs vary based on diet, health conditions, and environment. Thirst is generally a reliable indicator for healthy adults.

Key Sources: National Academies of Sciences Dietary Reference Intakes; Armstrong (2012) in Nutrition Reviews

📐 Body Fat Calculator

Method 1 - US Navy Formula:

• Men: 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
• Women: 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

Method 2 - BMI-based: Estimates using Deurenberg formula based on BMI, age, and sex

Limitations: Circumference methods are estimates with ±3-4% error. DEXA scans provide the most accurate body composition analysis.

Key Sources: Hodgdon & Beckett (1984) US Navy body composition equations; Deurenberg et al. (1991)

🏋️ One Rep Max Calculator

Methodology: Average of 5 validated 1RM prediction formulas

Formulas Used:

• Brzycki: weight × (36 / (37 − reps))
• Epley: weight × (1 + 0.0333 × reps)
• Lander: (100 × weight) / (101.3 − 2.67123 × reps)
• Lombardi: weight × reps^0.10
• O'Conner: weight × (1 + 0.025 × reps)

Limitations: Accuracy decreases above 10 reps. Formulas work best for compound lifts. Individual variation exists based on training experience and muscle fiber composition.

Key Sources: LeSuer et al. (1997) in Journal of Strength and Conditioning Research

🔥 Calorie Burn Calculator

Formula: Calories = MET × weight (kg) × duration (hours)

MET Values: Metabolic Equivalent of Task values from the Compendium of Physical Activities

• Walking (3 mph): 3.5 METs
• Running (6 mph): 9.8 METs
• Cycling (moderate): 8.0 METs
• Swimming (laps): 8.0 METs
• Weight training: 3.0-6.0 METs

Limitations: MET values are averages; actual burn depends on intensity, fitness level, and efficiency. Does not account for EPOC (afterburn effect).

Key Sources: Ainsworth et al. (2011) Compendium of Physical Activities

⏰ Intermittent Fasting Calculator

Methodology: Tracks fasting duration and maps metabolic states based on time since last meal

Fasting Stages:

• 4-8 hours: Blood sugar normalizes, insulin drops
• 12 hours: Glycogen depletion, ketosis begins
• 16-18 hours: Autophagy increases
• 24 hours: Enhanced autophagy, growth hormone surge

Limitations: Metabolic responses vary by individual. Timing of benefits is approximate. Not suitable for everyone—consult healthcare provider before starting.

Key Sources: de Cabo & Mattson (2019) in New England Journal of Medicine; Patterson & Sears (2017) in Annual Review of Nutrition

🧬 Biological Age Calculator

Methodology: Estimates biological age based on lifestyle factors known to affect aging markers

Factors Assessed:

• Exercise frequency: Up to −2 years
• Sleep quality: Up to −1 year
• Chronic stress: Up to +3 years
• Smoking: Up to +8 years
• Alcohol consumption: Up to +2 years
• Diet quality: Up to ±1 year
• Social connections: Up to ±1 year
• BMI: Up to +2 years

Limitations: This is an estimate based on lifestyle factors. True biological age requires clinical testing (DNA methylation, blood biomarkers). Use as a motivational tool, not a medical assessment.

Key Sources: Levine et al. (2018) in Aging; multiple longevity studies on lifestyle factors

❤️ Heart Risk Calculator

Methodology: 10-year cardiovascular disease risk estimation inspired by the Framingham Risk Score

Risk Factors:

• Age and sex
• Total cholesterol and HDL cholesterol
• Systolic blood pressure
• Smoking status
• Diabetes status
• Blood pressure medication use
• Family history of heart disease

Limitations: Simplified model for educational purposes. Clinical risk assessment (ASCVD Risk Calculator) should be used for medical decisions. Does not account for all risk factors.

Key Sources: D'Agostino et al. (2008) in Circulation; Framingham Heart Study

😤 Stress Score Calculator

Methodology: Assesses stress across 10 life domains with weighted scoring

Factors Assessed:

• Work/school pressure
• Job/financial security
• Relationship quality
• Financial concerns
• Health worries
• Sleep quality
• Recent life changes
• Sense of control
• Social support
• Relaxation time

Limitations: Self-reported assessment for general awareness. Not a clinical diagnostic tool. Validated instruments like PSS-10 should be used for clinical purposes.

Key Sources: Cohen's Perceived Stress Scale framework; Holmes-Rahe Stress Inventory concepts

📱 Screen Time Impact Calculator

Methodology: Calculates health impact based on screen time categories and mitigating factors

Categories Tracked:

• Work/school screen time
• Social media usage
• Streaming/video consumption
• Gaming
• General browsing
• Screen time before bed

Health Effects Assessed: Eye strain, sleep disruption, sedentary behavior, mental health impacts, posture issues

Limitations: Impact varies by individual. Quality and type of screen use matters. Not all screen time is equally harmful.

Key Sources: American Academy of Ophthalmology guidelines; research on digital wellness and sleep hygiene