Free Health Calculators
BMI, calorie needs, water intake, ideal weight, heart rate zones and more — all your health metrics calculated instantly, free and private.
About BMI Calculator
Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on height and weight. The formula is: BMI = Weight (kg) / Height (m)². For imperial units: BMI = 703 × Weight (lb) / Height (in)². WHO classification: Underweight (BMI < 18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), Obese Class III (≥ 40).
BMI is a useful population-level indicator but has limitations for individuals — it doesn't distinguish between muscle mass and fat mass, so athletes may be classified as overweight. Indian health guidelines suggest a lower cut-off (BMI > 23 = overweight) because South Asians have higher metabolic risk at lower BMI values. For a complete health picture, combine BMI with waist circumference, body fat percentage, blood pressure, and fasting glucose measurements.
About Calorie Calculator
Daily calorie needs are calculated from your Basal Metabolic Rate (BMR) multiplied by an activity factor. BMR is the energy your body needs at complete rest. Two main formulas: Mifflin-St Jeor (most accurate for most adults): Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5; Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161. Activity multipliers: Sedentary 1.2; Lightly active 1.375; Moderately active 1.55; Very active 1.725; Extremely active 1.9.
Calorie deficit and surplus guidelines: A deficit of 500 kcal/day produces approximately 0.5 kg fat loss per week (1 kg fat = 7,700 kcal). Deficits larger than 1,000 kcal/day risk muscle loss and nutrient deficiencies. For muscle gain, a 250-500 kcal surplus with adequate protein and resistance training is optimal (lean bulk). TDEE (Total Daily Energy Expenditure) = BMR x Activity Factor. Recalculate every 4-6 weeks as weight changes. Calorie estimates have a margin of error of 10-15%, so track actual results and adjust accordingly.
About Water Intake Calculator
Adequate hydration is essential for metabolism, kidney function, joint lubrication, and cognitive performance. The standard recommendation of 8 glasses (2 litres) per day is a rough guideline; actual needs vary significantly by body weight, activity level, climate, and diet. A common formula: Daily water (litres) = Body weight (kg) × 0.033. Add 350–500 ml for every 30 minutes of moderate exercise.
Signs of mild dehydration include dark urine, fatigue, headaches, and difficulty concentrating — these appear before you feel thirsty. About 20% of daily water intake comes from food (fruits, vegetables, soups). In hot climates or during intense exercise, electrolyte replacement (sodium, potassium) is as important as water volume to prevent hyponatraemia. The best hydration test: urine should be pale yellow. Use this calculator to set a personalised daily hydration target.
About Ideal Weight Calculator
Ideal body weight (IBW) is an estimate of a healthy target weight based on height and sex. Several validated formulas exist: Devine formula (most widely used, originally designed for drug dosing): Men: 50 kg + 2.3 kg per inch above 5 feet; Women: 45.5 kg + 2.3 kg per inch above 5 feet. Robinson formula: Men: 52 kg + 1.9 kg per inch above 5 feet; Women: 49 kg + 1.7 kg per inch. Our calculator shows results from multiple formulas for comparison.
Limitations of IBW: these formulas were developed from population averages and do not account for body composition, bone density, age, or ethnicity. A heavily muscled person may exceed their IBW while having excellent health. Healthy weight is better assessed using body fat percentage, waist circumference, or waist-to-height ratio (below 0.5 is generally healthy). BMI range 18.5-24.9 corresponds to a similar range but with the same limitations. IBW is most clinically useful for calculating medication doses and assessing nutritional status in clinical settings, not as a personal weight target.
About Heart Rate Zone Calculator
Heart rate training zones target different physiological adaptations. Maximum heart rate estimate: 220 minus age (standard) or 208 minus 0.7x age (Tanaka formula, more accurate for older adults). Training zones based on max HR: Zone 1 50-60% (recovery); Zone 2 60-70% (fat burning, aerobic base); Zone 3 70-80% (aerobic endurance); Zone 4 80-90% (anaerobic threshold, tempo); Zone 5 90-100% (maximum effort, VO2 max intervals).
Zone 2 training builds mitochondrial density and aerobic enzyme capacity and should comprise 70-80% of total training volume. Zone 4 training improves lactate threshold - the pace sustainable for approximately 1 hour. Monitor resting heart rate (normal 60-100 bpm; trained athletes often 40-60 bpm) - significantly elevated resting HR may indicate inadequate recovery or illness.
About Body Fat Percentage Calculator
Body fat percentage is a more accurate health indicator than BMI because it distinguishes fat mass from lean mass (muscle, bone, water, organs). Our calculator uses the US Navy tape measure method requiring waist, neck, and hip measurements - achieving approximately plus or minus 3-4% accuracy, comparable to bioelectrical impedance scales. The formula uses logarithms of the measurement differences.
Healthy body fat ranges: Men - Essential 2-5%, Athletic 6-13%, Fitness 14-17%, Average 18-24%, Obese 25%+. Women - Essential 10-13%, Athletic 14-20%, Fitness 21-24%, Average 25-31%, Obese 32%+. Women naturally carry more essential fat due to reproductive physiology. Track BFP monthly to assess whether training is building lean mass or losing fat - it provides more actionable data than scale weight alone.
About Sleep Calculator
Sleep quality depends not just on hours slept but on completing full sleep cycles. Each cycle lasts approximately 90 minutes and includes light sleep, deep sleep, and REM (Rapid Eye Movement) sleep. Waking mid-cycle causes sleep inertia — the grogginess of a "bad wake." This calculator finds optimal wake times by aligning your alarm with the end of a complete cycle.
Adults need 7–9 hours (4–6 full cycles). The first two cycles contain more deep sleep (critical for physical recovery and immune function); later cycles contain more REM sleep (critical for memory consolidation and emotional processing). Maintaining a consistent sleep and wake time — even on weekends — is the single most effective sleep improvement strategy, as it anchors your circadian rhythm. Avoid screens 1 hour before bed to prevent blue light suppression of melatonin.
About Macro Calculator
Macronutrients — protein, carbohydrates, and fat — are the three main energy sources in food. The right macro ratio depends on your goal: weight loss, muscle gain, or maintenance. Standard ratios by goal: Weight loss: 40% protein / 30% carbs / 30% fat; Muscle gain: 30% protein / 50% carbs / 20% fat; Maintenance: 25% protein / 50% carbs / 25% fat.
Caloric density: Protein = 4 kcal/g, Carbohydrates = 4 kcal/g, Fat = 9 kcal/g. High-protein diets (1.6–2.2g protein per kg bodyweight) are consistently shown to improve body composition and preserve muscle during caloric restriction. For a 70 kg person targeting 2,000 kcal: 40% protein = 200g protein, 30% carbs = 150g carbs, 30% fat = 67g fat. Use this tool alongside our Calorie Calculator for a complete nutrition plan.
About Pregnancy Due Date Calculator
The estimated due date (EDD) is calculated by Naegele rule: add 40 weeks (280 days) to the first day of your last menstrual period (LMP). This assumes a regular 28-day cycle with ovulation on day 14. For cycles other than 28 days, adjust the EDD by the difference from 28 days. Gestational age is counted from the LMP, not from conception - which is approximately 2 weeks after LMP.
Pregnancy trimesters: First trimester weeks 1-12 (critical organ development); Second trimester weeks 13-26 (growth period, typically most comfortable); Third trimester weeks 27-40 (rapid growth, preparation for birth). Only approximately 5% of babies are born on their exact EDD - normal delivery is 37-42 weeks. An ultrasound at 8-12 weeks provides the most accurate dating when cycle length is irregular. Always confirm dates with your gynaecologist.
About Ovulation Calculator
Ovulation is the release of a mature egg from the ovary, occurring approximately 12-16 days before the start of the next menstrual period. Our calculator predicts ovulation date and fertile window from the first day of your last period and average cycle length. The luteal phase (ovulation to next period) is typically consistent at 12-16 days even when cycle length varies.
Ovulation tracking methods by reliability: Ovulation predictor kits (OPKs) detecting LH surge: 97% accuracy 24-48 hours before ovulation; Cervical mucus monitoring: 70-80% accuracy; Calendar method alone: approximately 60-75% accuracy for regular cycles. Stress, illness, travel, and weight changes can shift ovulation by several days. Polycystic ovary syndrome (PCOS) causes irregular or absent ovulation and reduces prediction reliability. Confirm ovulation with OPKs or ultrasound if actively trying to conceive.
About Calories Burned Calculator
Calories burned during exercise is estimated using MET (Metabolic Equivalent of Task) values. Formula: Calories/hour = MET x Body Weight (kg) x 3.5 / 200 x 60. MET values represent intensity relative to resting metabolism (1 MET): Walking 3.5 km/h = 2.5 MET; Cycling moderate = 8.0 MET; Running 8 km/h = 8.3 MET; Swimming laps moderate = 7.0 MET; Yoga = 2.5 MET; HIIT = 8.0-12.0 MET; Strength training = 3.5-6.0 MET.
Exercise calorie estimates have significant variability (up to 30-40%) due to individual differences in fitness level, movement efficiency, and body composition. Heart rate-based methods (using actual HR data from a chest strap or fitness tracker) are more accurate than formula estimates. Post-exercise oxygen consumption (EPOC or afterburn) adds an additional 6-15% calorie burn for high-intensity sessions, lasting up to 48 hours. Do not over-rely on calorie burn estimates for weight management - compensation effects (eating more and moving less after exercise) can negate up to 70% of exercise calorie deficit in some individuals.
About Running Pace Calculator
Running pace is measured as time per kilometre (or per mile). This calculator converts between pace, speed, and total time for any distance. Common race distances: 5K (3.1 miles), 10K (6.2 miles), half marathon (21.1 km), and marathon (42.2 km). The Riegel formula projects equivalent performance across distances: Time2 = Time1 x (Distance2 / Distance1)^1.06.
Pace training zones: Easy run pace is typically 60-75 sec/km slower than 5K race pace. Tempo run pace is approximately your 1-hour race pace. Long run pace is 90 sec to 2 min/km slower than marathon pace. Cadence and stride length both affect pace - most elite runners maintain 170-180 steps per minute. Increasing cadence by 5-10% reduces injury risk by lowering ground contact time and vertical oscillation.
About Blood Pressure Analyser
Blood pressure is recorded as systolic (pressure when heart beats) over diastolic (pressure between beats) in mmHg. WHO/AHA classification: Normal below 120/80; Elevated 120-129 and below 80; Stage 1 Hypertension 130-139 or 80-89; Stage 2 Hypertension 140+ or 90+; Hypertensive Crisis above 180 or above 120. Hypotension is typically below 90/60 mmHg.
Measurement accuracy tips: sit quietly for 5 minutes before measuring; keep the cuff at heart level; avoid caffeine, exercise, or smoking 30 minutes before; take readings on the same arm at the same time each day. White coat hypertension affects approximately 20% of people - home monitoring is more reliable for diagnosis. Lifestyle factors that significantly reduce BP: weight loss (1 mmHg per kg), regular aerobic exercise, reducing sodium intake, DASH diet, and limiting alcohol. Always consult a doctor before interpreting BP readings for medical decisions.
About Waist-to-Hip Ratio Calculator
Waist-to-Hip Ratio (WHR) is calculated by dividing waist circumference by hip circumference. It is a better predictor of cardiovascular disease and metabolic syndrome risk than BMI because it specifically measures abdominal (visceral) fat distribution. Visceral fat surrounds internal organs and is metabolically active, releasing inflammatory markers and fatty acids directly into the portal circulation.
WHO risk thresholds: Men - Low risk below 0.95, Moderate 0.96-1.0, High above 1.0; Women - Low risk below 0.80, Moderate 0.81-0.85, High above 0.85. Measure waist at the narrowest point between ribs and hip bone. Measure hips at the widest point across the buttocks. Apple-shaped body types with high WHR carry significantly higher risk of type 2 diabetes, hypertension, and coronary heart disease compared to pear-shaped (low WHR) body types with the same BMI.
About VO2 Max Estimator
VO2 max is the maximum rate of oxygen consumption during intense exercise, measured in mL O2 per kg body weight per minute. It is the gold standard measure of cardiovascular fitness. Our calculator estimates VO2 max from sub-maximal exercise tests (such as a 1.5-mile run time or step test heart rate) using validated equations without requiring laboratory equipment.
VO2 max percentile ranges for men: Poor below 35, Fair 35-42, Good 43-52, Excellent 53-60, Superior above 60. Values for women are approximately 10-15% lower due to differences in haemoglobin concentration and lean body mass. VO2 max improves 5-15% with consistent aerobic training over 3-6 months. High-intensity interval training (HIIT) and zone 4-5 efforts are most effective at improving VO2 max. Elite marathon runners typically score 70-85 mL/kg/min.
About Protein Intake Calculator
Protein requirements depend on body weight, activity level, and goal. Guidelines: Sedentary adults 0.8g/kg (RDA minimum); Recreational exercisers 1.2-1.6g/kg; Endurance athletes 1.4-1.7g/kg; Strength athletes 1.6-2.2g/kg; Weight loss with muscle preservation 1.8-2.4g/kg; Older adults 1.2-1.6g/kg (higher due to anabolic resistance).
Protein timing matters for muscle protein synthesis: consuming 20-40g within 2 hours post-exercise maximises recovery. Distribute protein evenly across 3-5 meals - the body cannot utilise more than approximately 40g at once for muscle synthesis. Complete protein sources (all essential amino acids): eggs, dairy, meat, fish, soy, and quinoa. Plant-based athletes should combine sources (rice plus lentils, for example) to achieve complete amino acid profiles.
About Keto Macro Calculator
The ketogenic diet maintains carbohydrate intake below 20-50g per day to induce ketosis - a metabolic state where the liver produces ketone bodies from fat as the primary fuel source. Standard keto macro split: Fat 65-75% of calories, Protein 20-30%, Carbohydrates 5-10%. This calculator computes personalised daily macro targets based on calorie goals, activity level, and body composition.
Ketosis is typically achieved within 2-4 days of restricting carbohydrates below 50g/day. Common side effects in the first week (keto flu): headache, fatigue, and brain fog due to electrolyte shifts. Increase sodium (3-5g/day), potassium, and magnesium intake to mitigate these effects. Net carbs = total carbs minus dietary fibre. Keto is effective for weight loss and blood sugar management, but consult a doctor if you have diabetes, kidney disease, or pancreatic conditions before starting.
About Intermittent Fasting Calculator
Intermittent fasting (IF) cycles between eating windows and fasting periods. Common protocols: 16:8 (fast 16 hours, eat within 8-hour window - most popular); 18:6 (more aggressive, shorter eating window); 5:2 (eat normally 5 days, restrict to 500-600 calories on 2 non-consecutive days); OMAD (one meal a day). Our calculator identifies eating window, fasting start/end times, and tracks adherence.
Metabolic benefits of fasting begin after approximately 12 hours: glycogen stores deplete and fat oxidation increases. At 18-24 hours, autophagy (cellular repair) is upregulated. IF works primarily through calorie restriction and does not require changing food composition. Black coffee, tea, and water do not break a fast. People with diabetes, eating disorder history, or who are pregnant should consult a doctor before attempting IF.
About Steps to Calories Calculator
This calculator converts daily step count to estimated calorie burn using stride length, body weight, and step cadence. Average stride length is approximately 0.415 x height in metres. Walking speed affects calorie burn: brisk walking (5-6 km/h) burns approximately 30% more calories per step than slow walking (3 km/h) due to increased energy expenditure per unit distance.
The widely cited 10,000 steps per day target originated from a 1960s Japanese pedometer marketing campaign, not clinical research. Recent studies show significant health benefits at 7,000-8,000 steps per day, with diminishing returns above 10,000 steps for most populations. Walking 8,000 steps burns approximately 300-400 calories for a 70kg person. Combining step targets with intensity - including 15-30 minutes of brisk walking within the daily total - provides greater cardiovascular benefit than total step count alone.
About Sleep Debt Calculator
Sleep debt is the cumulative deficit between sleep obtained and sleep needed. It accumulates when you consistently sleep less than your biological requirement. Adult sleep requirements: 7-9 hours for most adults (18-64 years); 7-8 hours for 65+ years. Our calculator tracks daily sleep logs over a week and computes total sleep debt against your personal baseline requirement.
Sleep debt effects: cognitive impairment from 17 hours of wakefulness equals BAC of 0.05%; 24 hours wakefulness equals BAC of 0.10%. Chronic short sleep (below 6 hours) is associated with 30% higher risk of obesity, impaired glucose regulation, elevated cortisol, and increased cardiovascular disease risk. Recovery from sleep debt: moderate debt (under 10 hours) can be partially recovered with 2-3 nights of extended sleep. Severe chronic debt requires weeks of adequate sleep to fully restore cognitive function. Weekend catch-up sleep reduces but does not eliminate health risks of weekly sleep restriction. Maintain consistent sleep and wake times even on weekends to preserve circadian rhythm stability.
About Muscle Mass Calculator
Muscle mass (skeletal muscle mass) is calculated from total body weight, body fat percentage, and non-muscle lean mass (bone, organs, water). Our calculator uses the Lee formula: SMM = height^2 x (thigh circ x 0.031 + calf circ x 0.033 - age x 0.014 + sex constant). Alternatively, if BFP is known: Lean Mass = Weight x (1 - BFP), then subtract bone and organ mass estimates.
Average skeletal muscle mass as percentage of body weight: Men 38-54%, Women 28-39%. Muscle mass peaks in the late 20s and declines approximately 3-8% per decade after age 30 (sarcopenia), accelerating after 60. Resistance training 2-3 times per week is the most effective intervention to maintain and build muscle mass across all ages. Adequate protein intake (1.6-2.2g/kg) combined with progressive overload is the evidence-based approach for muscle hypertrophy.
About Vitamin D Calculator
Vitamin D is synthesised in the skin upon exposure to UVB radiation (wavelength 290-315 nm). Our calculator estimates daily vitamin D production from sun exposure based on latitude, season, time of day, skin type, and exposed skin area. UVB intensity varies significantly: near-zero in winter above 35 degrees latitude, peak intensity from 10am-2pm, and blocked by SPF15 sunscreen by approximately 93%.
Vitamin D status by serum 25(OH)D: Deficient below 20 ng/mL (50 nmol/L); Insufficient 20-29 ng/mL; Sufficient 30-60 ng/mL; Optimal for athletes 40-60 ng/mL; Toxic above 150 ng/mL. In India, despite abundant sunshine, deficiency affects approximately 70-80% of the population due to indoor lifestyles, dark skin, and air pollution reducing UVB penetration. Supplementation of 1000-2000 IU/day is safe for most adults; test serum levels before high-dose supplementation.
About Child Growth Percentile Calculator
Child growth percentiles compare a child height, weight, and BMI against WHO or CDC reference populations of the same age and sex. Percentile indicates percentage of children at or below that measurement - 50th percentile is average, 85th means taller or heavier than 85% of peers. Our calculator uses WHO Child Growth Standards (birth to 5 years) and WHO Reference (5-19 years).
A single measurement matters less than the growth trajectory over time. Consistently tracking along any percentile curve (5th to 95th) is generally normal. Concern arises when a child crosses two major percentile lines in either direction, which may indicate nutritional, hormonal, or medical issues. BMI-for-age: below 5th percentile is underweight; 85th-95th is overweight; above 95th is obese. Always interpret growth data with a paediatrician who has the full clinical context.
Rate each question: 0 = Never, 1 = Almost Never, 2 = Sometimes, 3 = Fairly Often, 4 = Very Often
About Stress Level Assessment
This stress assessment uses validated psychometric scales including the Perceived Stress Scale (PSS-10) and questions derived from the Holmes-Rahe Stress Inventory to estimate your current stress burden. The PSS-10 measures the degree to which situations in your life are perceived as stressful. Scores: 0-13 Low stress, 14-26 Moderate stress, 27-40 High perceived stress.
Physiological effects of chronic stress: elevated cortisol impairs immune function, disrupts sleep, increases abdominal fat deposition, and raises cardiovascular disease risk. Evidence-based stress reduction: progressive muscle relaxation, box breathing (4 counts in, 4 hold, 4 out, 4 hold), regular aerobic exercise (reduces cortisol), social connection, and mindfulness meditation (minimum 8-week practice shows measurable cortisol reduction). Persistent high stress scores warrant consultation with a mental health professional or GP for evidence-based interventions.
About Posture and Ergonomics Calculator
Poor posture causes mechanical stress on the spine, muscles, and joints. Our calculator evaluates your workstation setup against ergonomic standards and identifies risk factors for musculoskeletal disorders. Key measurements: monitor top at or slightly below eye level; screen distance 50-70cm; elbow angle 90-110 degrees; hip angle 90-110 degrees; feet flat on floor or footrest.
Forward head posture increases effective head weight on the cervical spine: at 15 degrees forward tilt, effective load is 12kg (vs 5kg neutral); at 45 degrees, effective load is 22kg. Sitting compresses lumbar discs 40% more than standing. Evidence-based interventions: microbreaks every 30-45 minutes (stand or walk for 2-5 minutes); proper monitor and keyboard positioning; lumbar support maintaining natural lordosis; strengthening posterior chain and stretching hip flexors. Standing desks should alternate with sitting rather than replace it entirely.
About Fertility Window Calculator
The fertility window is the 6-day period ending on ovulation day (the day of ovulation plus the 5 preceding days). Sperm survives 3-5 days in the female reproductive tract; an egg survives 12-24 hours after ovulation. For a 28-day cycle, ovulation typically occurs around day 14. For irregular cycles, ovulation typically occurs 12-16 days before the next expected period.
Signs of approaching ovulation: increase in cervical mucus (clear, stretchy, egg-white consistency); slight rise in basal body temperature (0.2-0.5 degrees C) after ovulation; positive LH surge on ovulation predictor kit 24-48 hours before ovulation. Basal body temperature charting requires measuring temperature immediately upon waking before any activity. Irregular cycles warrant a fertility specialist consultation if conception is the goal.
About Alcohol Units Calculator
Alcohol units standardise measurement of alcohol intake. One UK unit = 10mL (8g) of pure alcohol. Formula: Units = (Volume mL x ABV%) / 1000. Common drinks: Pint of 4% beer = 2.3 units; 175mL glass of 13% wine = 2.3 units; 25mL shot of 40% spirits = 1 unit; 330mL can of 5% beer = 1.7 units.
UK Chief Medical Officers low-risk guideline: no more than 14 units per week, spread over 3+ days, with at least 2 alcohol-free days per week. Above 14 units weekly increases risk of liver disease, cancers (mouth, throat, breast, bowel), and cardiovascular disease. Alcohol is metabolised at approximately 1 unit per hour regardless of food, coffee, or exercise. Blood Alcohol Content (BAC) peaks 30-90 minutes after drinking. The calculator also estimates time to zero BAC using the Widmark formula adjusted for body weight and sex.
About Medicine Dosage Calculator
This calculator computes weight-based paediatric and adult medication dosages using the formula: Dose = Weight (kg) x Dose per kg (mg/kg). Common weight-based dosing examples: Paracetamol 10-15 mg/kg every 4-6 hours (max 60 mg/kg/day); Ibuprofen 5-10 mg/kg every 6-8 hours (max 40 mg/kg/day); Amoxicillin 25-45 mg/kg/day divided every 8 hours.
Important: This calculator is a reference tool only - always verify dosage with a registered pharmacist or physician before administering. Doses for renally or hepatically impaired patients require adjustment. Maximum adult doses apply regardless of weight above approximately 50kg for most drugs. Paediatric dosing differs significantly from adult dosing due to differences in drug metabolism and elimination. Never exceed stated maximum doses. For emergency situations always contact a healthcare provider immediately.
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