Medical & Clinical Calculators

10 free evidence-based medical calculators: BMI, BMR/TDEE, eGFR kidney staging, BSA drug dosing, QTc interval, IV drip rate, MAP blood pressure, pregnancy due date, weight gain & BAC. No signup required.

BMI Calculator

Calculate Body Mass Index using WHO-standard formula with category classification and ideal weight range.

Live Results Updates instantly
Body Mass Index (BMI)
22.9
Normal Weight

Detailed Metrics

Ideal Weight (Devine)
65.0–75.0 kg
Health Risk Level
Low
BMI Category
Normal Weight
Weight to Ideal (mid)
0 kg
Expert Reviewed & Clinically Validated for 2026

The Complete Guide to Medical & Clinical Calculations

From calculating your BMI and kidney function to dosing chemotherapy by BSA and monitoring QTc safety in hospital settings — master every clinical formula with evidence-based guidance.

01Body Mass Index: The Complete Clinical Interpretation Guide

Body Mass Index was developed in the 1830s by Adolphe Quetelet as a population-level statistical tool, never intended for individual clinical diagnosis. Despite this origin, BMI became the global standard for obesity classification due to its simplicity: weight in kilograms divided by height in metres squared. Every healthcare system, insurance company, and research institution uses it — making it essential to understand precisely what it measures, and crucially, what it does not.

22.9
Average Adult BMI (US)
42%
US Adults Obese (BMI≥30)
18.5–24.9
Normal BMI Range
23
Asian Obesity Threshold

WHO BMI Classification Table

Standard WHO Categories
  • <18.5 — Underweight (Malnutrition risk)
  • 18.5–24.9 — Normal weight (Lowest risk)
  • 25.0–29.9 — Overweight (Elevated risk)
  • 30.0–34.9 — Obese Class I (High risk)
  • 35.0–39.9 — Obese Class II (Very high)
  • ≥40.0 — Obese Class III (Extreme risk)
Asian-Specific Thresholds (WHO 2004)
  • <18.5 — Underweight
  • 18.5–22.9 — Normal weight
  • 23.0–27.4 — Overweight (increased risk)
  • ≥27.5 — Obese (high risk)
  • Note: Same metabolic risks occur at lower BMI in South Asian, East Asian, and Southeast Asian populations.
BMI Limitations: BMI cannot distinguish between muscle mass and fat mass. A professional rugby player with 8% body fat may have a BMI of 28 (overweight). Conversely, an elderly person with a BMI of 23 may have sarcopenic obesity (high fat, low muscle). Always combine BMI with waist circumference (<88 cm women, <102 cm men) and clinical assessment.

Ideal Body Weight Formulas

The Devine formula (1974) is most widely used clinically for drug dosing, ventilator settings, and nutritional support:

Devine Formula
Male: 50 + 2.3×(height_in − 60)
Female: 45.5 + 2.3×(height_in − 60)
Example: 5'9" male = 50 + 2.3×9 = 70.7 kg
Hamwi Formula
Male: 48 + 2.7×(height_in − 60)
Female: 45.5 + 2.2×(height_in − 60)
±10% for frame size variation

Waist Circumference: The Missing Dimension

The World Health Organization and major cardiology bodies now recommend combining BMI with waist circumference for metabolic risk assessment. Waist circumference directly reflects visceral adiposity — the fat packed around organs that drives insulin resistance, systemic inflammation, and cardiovascular disease far more aggressively than subcutaneous fat. Regardless of BMI, a waist circumference >88 cm in women or >102 cm in men is classified as high metabolic risk by both the American Heart Association and the European Society of Cardiology.

The waist-to-height ratio (WHtR) offers another practical screening tool: a ratio below 0.5 is associated with substantially lower cardiometabolic risk in most populations. This measure is particularly useful in South Asian and East Asian populations, where standard BMI cutoffs systematically underestimate metabolic risk — a 55 kg woman at 158 cm with a BMI of 22.0 may still carry high visceral fat and significant metabolic syndrome components.

Clinical Pearl: The Edinburgh Body Composition Study found that 29% of people with a "normal" BMI (18.5–24.9) had metabolically obese profiles, while 48% of people classified as "obese" by BMI had metabolically healthy profiles. This is why BMI is a screening tool, not a diagnostic tool — and why the full clinical picture always requires physical examination and laboratory testing.

02BMR & TDEE: The Mathematics of Energy Balance

Every kilogram of fat lost or gained represents approximately 7,700 kcal of deficit or surplus. Understanding your Basal Metabolic Rate and Total Daily Energy Expenditure is the fundamental prerequisite for any evidence-based nutrition plan. These numbers are not estimates to be dismissed — they are the metabolic constants around which every successful body composition change is engineered.

1,600–2,000
Avg Female BMR (kcal)
1,800–2,200
Avg Male BMR (kcal)
−500 kcal
~0.5 kg/wk fat loss
7,700 kcal
Per kg of body fat

Mifflin-St Jeor vs. Harris-Benedict

The Mifflin-St Jeor equation (1990) is the most validated formula for resting energy expenditure in non-obese adults, with a mean error of only 10% in controlled studies. The original Harris-Benedict equations (1919) overestimate BMR by 5% in modern populations due to changes in average body composition over the past century.

✓ Mifflin-St Jeor (Recommended)
Male: (10×W) + (6.25×H) − (5×A) + 5
Female: (10×W) + (6.25×H) − (5×A) − 161
W=kg, H=cm, A=years
Harris-Benedict (1919, legacy)
Male: 88.4 + 13.4W + 4.8H − 5.68A
Female: 447.6 + 9.25W + 3.1H − 4.33A
~5% overestimate vs. Mifflin
Activity Multiplier Reference: Sedentary (×1.2) | Light exercise (×1.375) | Moderate (×1.55) | Very active (×1.725) | Athlete/2×/day (×1.9). A common error is overestimating activity level — most desk workers should use ×1.2 to ×1.375 even if they exercise 3–4 times per week.

Macro Distribution Strategies

Once TDEE is established, macro distribution determines body composition change speed and muscle preservation. For fat loss, protein should be elevated to 1.6–2.4 g/kg of body weight (per the IAAO method), higher than the old 0.8 g/kg RDA, to maximally protect lean mass during caloric restriction. Carbohydrates should scale with training intensity — rest days warrant fewer carbs (1–3 g/kg), training days more (3–6 g/kg). Dietary fat should not drop below 0.5 g/kg to protect testosterone, vitamin absorption, and cell membrane integrity.

For muscle gain (bulking), a surplus of 200–400 kcal above TDEE is optimal for experienced trainees — larger surpluses primarily add fat, not muscle. Protein at 1.6–2.2 g/kg is sufficient; additional protein beyond this point adds cost without proportional benefit for muscle protein synthesis. The timing of protein matters too: distributing 0.4 g/kg across 4–5 meals maximizes muscle protein synthesis through the leucine threshold mechanism.

2.0 g/kg
Protein for fat loss
200–400 kcal
Optimal bulk surplus
7,700 kcal
Per kg of body fat
0.5 g/kg min
Fat floor (hormonal)

03eGFR & Chronic Kidney Disease: Staging for Clinical Action

The kidneys filter approximately 180 litres of blood per day. When this filtration capacity declines, waste products accumulate, electrolytes become dysregulated, blood pressure rises, and erythropoietin production falls — leading to anemia. The estimated Glomerular Filtration Rate is the single most important measure of kidney function, used globally to stage CKD and guide therapeutic decisions.

≥90
Stage G1 (Normal)
60–89
Stage G2 (Mild)
30–59
Stage G3 (Moderate)
<15
Stage G5 (Failure)
CKD-EPI 2021 Race-Free Equation: eGFR = 142 × min(Scr/κ, 1)¹ × max(Scr/κ, 1)^(−1.200) × 0.9938^Age × (1.012 if female). Where κ = 0.7 (female) or 0.9 (male), and α = −0.241 (female) or −0.302 (male). The 2021 update removed race as a variable, addressing health equity concerns identified in the 2009 equation.

CKD Staging and KDIGO Clinical Actions

G1 & G2: Monitor
  • G1 (≥90): Normal — treat underlying disease
  • G2 (60–89): Mildly decreased — annual eGFR monitoring
  • Blood pressure target: <130/80 mmHg
  • RAAS inhibitor therapy if proteinuria present
G4 & G5: Urgent Action
  • G4 (15–29): Severe — nephrology referral mandatory
  • G5 (<15): Failure — prepare for RRT or transplant
  • Avoid nephrotoxic drugs (NSAIDs, contrast agents)
  • Adjust drug doses for reduced clearance

Albuminuria & the Two-Dimensional CKD Grid

eGFR alone is insufficient for complete CKD staging. KDIGO 2012 guidelines introduced a two-dimensional grid combining eGFR stages (G1–G5) with albuminuria categories (A1: <30 mg/g, A2: 30–300 mg/g, A3: >300 mg/g). A patient with eGFR of 75 (Stage G2) but albuminuria of 450 mg/g (Category A3) carries substantially higher cardiovascular mortality risk than a patient with the same eGFR and A1 albuminuria. The combination of G3b A3 carries the same mortality risk as many G5 patients.

Serum cystatin C is the most accurate filtration marker when creatinine is unreliable due to extremes of muscle mass (bodybuilders, amputees, severely malnourished patients). The CKD-EPI creatinine-cystatin C equation combines both markers for the highest GFR accuracy available without direct measurement. Direct GFR measurement using iohexol, iothalamate, or 99mTc-DTPA clearance remains the gold standard but is impractical outside research settings.

Nephrotoxic Drug Alert: At eGFR <30, dose adjustment is required for metformin (stop), many antibiotics (fluoroquinolones, aminoglycosides), direct oral anticoagulants (dabigatran, rivaroxaban), and SGLT2 inhibitors (reduced efficacy, stop at G4). NSAIDs are contraindicated at all CKD stages due to afferent arteriole vasoconstriction reducing GFR further. Contrast agents should be used with caution at eGFR <30 even with iso-osmolar agents.

04Body Surface Area: Precision Drug Dosing in Oncology

Body Surface Area is used for drug dosing because many chemotherapy agents have a narrow therapeutic index: too little and the cancer survives; too much and the patient develops life-threatening toxicity. By normalizing doses to BSA rather than weight alone, pharmacologists discovered they could reduce inter-patient variability in drug exposure by approximately 25–40%.

1.73 m²
Reference BSA (standard)
1.9 m²
Average Adult Male
1.6 m²
Average Adult Female
±15%
BSA variability vs. weight
Mosteller Formula (Oncology standard): BSA = √[Height(cm) × Weight(kg) / 3600]. Simple, widely validated, preferred by ASCO guidelines. DuBois & DuBois (1916) = 0.007184 × H^0.725 × W^0.425 — historically standard but less accurate. Haycock (1978) = 0.024265 × H^0.3964 × W^0.5378 — best validated in pediatric populations.

Limitations of BSA-Based Dosing

Despite its dominance in oncology, BSA-based dosing has a well-documented limitation: it fails to account for the metabolic variability that actually determines drug clearance. Two patients with identical BSA of 1.73 m² may differ by 30–40-fold in cytochrome P450 enzyme activity due to genetic polymorphisms, age-related hepatic changes, and drug-drug interactions. This is why therapeutic drug monitoring (TDM) is standard practice for agents like 5-fluorouracil, where individualized dosing based on AUC rather than BSA has been shown in multiple trials to reduce toxicity without compromising efficacy.

For obese patients, whether to use actual body weight or ideal/adjusted body weight in BSA calculations remains debated. Most oncology protocols specify which weight to use; using actual weight in severely obese patients can result in supra-therapeutic doses. ASCO guidelines recommend using actual body weight for most cytotoxic agents unless the treating oncologist documents clinical reasoning for dose capping.

Pediatric Note: In children under 10 kg, BSA-based dosing is particularly unreliable due to the non-linear relationship between body size and drug clearance in neonates and infants. Weight-based dosing (mg/kg) is preferred for this population, and the Haycock formula provides the most accurate BSA estimates in children under 5 years.

05QTc Interval & Torsades de Pointes Prevention

The QT interval represents ventricular depolarization and repolarization. When corrected for heart rate (QTc), it is the most important surrogate marker for the risk of torsades de pointes (TdP) — a polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation and sudden death. Hundreds of commonly prescribed drugs prolong the QTc interval, making this calculation critical in polypharmacy management.

<440 ms
Normal (Male)
<450 ms
Normal (Female)
440–500 ms
Borderline Prolonged
>500 ms
TdP Risk (Critical)
High-Risk QT-Prolonging Drug Combinations: Azithromycin + citalopram, ondansetron + sotalol, haloperidol + methadone. Check CredibleMeds (www.crediblemeds.org) before prescribing. Risk is amplified by hypokalemia, hypomagnesemia, bradycardia, and female sex.

Bazett vs. Fridericia: Which Formula to Use?

Bazett's formula (QTc = QT/√RR) over-corrects at high heart rates (>100 bpm) and under-corrects at low rates (<60 bpm). Fridericia's formula (QTc = QT/RR^(1/3)) performs better at extreme heart rates. Framingham's linear correction (QTc = QT + 0.154×(1−RR)) is best for population studies. For bedside clinical use, Bazett remains the default because all reference ranges are published against it.

When to Obtain an ECG and Act

Routine ECG before starting any QT-prolonging agent is recommended by most cardiology guidelines when baseline QTc is unknown, the patient is female, elderly, or has structural heart disease. Serial ECG monitoring is mandatory when combining two or more QT-prolonging agents, when QTc is found to be 440–470 ms at baseline, or when electrolytes are abnormal. Hypokalemia (K<3.5 mEq/L) and hypomagnesemia (<0.7 mmol/L) potentiate QT prolongation independently of drug effects — correcting these abnormalities is the first step before dose reduction.

The FDA's Thorough QT/QTc Study (ICH E14 guidance) requires all new non-cardiac drugs to demonstrate they do not cause >5 ms mean QTc prolongation vs. placebo in healthy volunteers. A drug that prolongs QTc by >20 ms in any individual or >10 ms on average is typically flagged for cardiac safety review. This regulatory framework exists specifically because fatal arrhythmias from drug interactions (e.g., the withdrawn cisapride, terfenadine, thioridazine) cost lives before systematic monitoring existed.

06IV Drip Rate Calculation: The Nursing Safety Formula

Incorrect IV drip rate calculation is a leading cause of preventable medication errors in hospital settings. The fundamental formula is: Drip Rate (gtts/min) = Volume (mL) × Drop Factor (gtts/mL) ÷ Time (min). Mastering this formula is a core nursing competency required for all clinical settings, particularly critical care.

10–15 gtts/mL
Macro-drip (standard adult)
20 gtts/mL
Macro-drip (common)
60 gtts/mL
Micro-drip (pediatric)
<5% error
Acceptable rounding range
Example Calculation: 1,000 mL NS over 8 hours using 20 gtts/mL set. Drip rate = 1,000 × 20 / (8 × 60) = 20,000 / 480 = 41.7 ≈ 42 gtts/min. For electronic infusion pumps: simply 1,000 / 8 = 125 mL/hr.

High-Alert Medications Requiring Pump-Only Administration

The Institute for Safe Medication Practices (ISMP) identifies specific medications that should never be administered by gravity drip without an electronic infusion pump with dose-error reduction software (DERS/smart pump). These include: concentrated potassium chloride (>10 mEq/hr), heparin infusions, insulin infusions, neuromuscular blocking agents, opioid infusions, magnesium sulfate, and concentrated sodium chloride (>0.9%). For these medications, the manual drip rate calculation serves as a verification check against the pump setting — not as a primary administration method.

Standard Drop Factors
  • 10 gtts/mL — Macro-drip (blood products)
  • 15 gtts/mL — Macro-drip (common adult)
  • 20 gtts/mL — Macro-drip (most common)
  • 60 gtts/mL — Micro-drip (pediatric/precise)
High-Alert Medications (Pump Only)
  • Concentrated KCl (>10 mEq/hr)
  • IV heparin and insulin infusions
  • Neuromuscular blocking agents
  • Concentrated NaCl (>0.9%)

07Mean Arterial Pressure & Blood Pressure Classification

Mean Arterial Pressure represents the average pressure driving blood through the systemic circulation during the entire cardiac cycle. Because diastole lasts twice as long as systole, MAP is not a simple average: MAP = DBP + (SBP − DBP)/3. A MAP below 60 mmHg is a clinical emergency — the threshold below which the brain, kidneys, and heart can no longer receive adequate perfusion.

AHA 2017 BP Categories
  • Normal: <120/<80 mmHg
  • Elevated: 120–129/<80 mmHg
  • Stage 1 HTN: 130–139/80–89
  • Stage 2 HTN: ≥140/≥90 mmHg
  • Crisis: >180/>120 (emergency)
MAP Clinical Thresholds
  • <60 mmHg: Organ perfusion failure
  • 65 mmHg: Septic shock target minimum
  • 70–100 mmHg: Normal range
  • >110 mmHg: Hypertensive, monitor closely
  • >130 mmHg: Hypertensive urgency/emergency

Ambulatory Blood Pressure Monitoring & White-Coat Hypertension

Office blood pressure measurements overestimate true blood pressure in 15–30% of patients due to white-coat hypertension — an alerting response triggered by the clinical setting. Ambulatory blood pressure monitoring (ABPM) over 24 hours is the gold standard for diagnosing sustained hypertension and is more predictive of cardiovascular events than isolated office readings. Awake mean BP >135/85 mmHg or 24-hour mean >130/80 mmHg on ABPM is diagnostic of hypertension, even if office readings appear normal.

Masked hypertension — normal office readings but elevated ABPM — affects approximately 10–15% of people and carries cardiovascular risk equivalent to sustained hypertension. Home blood pressure monitoring (HBPM) captures masked hypertension better than office readings and is now recommended for treatment monitoring by ESC/ESH 2023 guidelines. The optimal technique: morning readings taken after 5 minutes rest, bladder empty, seated, arm supported at heart level, two readings 1–2 minutes apart, averaged over 7 days.

08Pregnancy Due Date: Naegele's Rule & Gestational Age

Naegele's Rule adds 280 days (40 weeks) to the first day of the last menstrual period — an approximation based on the assumption of a 28-day cycle with ovulation on day 14. Only 4% of babies are born on their exact EDD. The normal delivery window spans from 37 weeks 0 days (early term) through 41 weeks 6 days. Ultrasound dating between 8–13+6 weeks is more accurate than LMP dating when there is a discrepancy of more than 5–7 days.

280 days
LMP to EDD (Naegele)
266 days
Conception to EDD
Wk 1–12
1st Trimester
Wk 13–26
2nd Trimester
Cycle Length Adjustment: For cycles longer than 28 days, add the excess days to the EDD. For a 32-day cycle, add 4 days to the Naegele calculation. For a 25-day cycle, subtract 3 days. This adjustment is automatically applied in this calculator.

Ultrasound Dating & Growth Scans

First-trimester ultrasound (crown-rump length at 8–13+6 weeks) is the most accurate dating method, with a margin of error of only ±3–5 days. Second-trimester ultrasound (biparietal diameter, femur length at 14–20 weeks) has a wider margin (±7–14 days) and is used to confirm or adjust LMP dating if the difference exceeds 10 days. Third-trimester dating is least accurate (±21 days) and should only revise the EDD if no prior ultrasound is available.

The anatomy scan at 18–22 weeks evaluates fetal organ development and screens for structural anomalies. Third-trimester growth scans at 28, 32, and 36 weeks monitor estimated fetal weight and amniotic fluid index — serial measurements are more informative than single readings for identifying intrauterine growth restriction (IUGR), defined as estimated fetal weight below the 10th percentile with abnormal Doppler velocimetry.

Wk 10–13
NIPT / CVS window
Wk 18–22
Anatomy scan
Wk 24
Viability threshold
Wk 37–42
Term delivery window

09BAC & Alcohol Pharmacokinetics

Blood Alcohol Content is a direct measure of the concentration of ethanol in the bloodstream. The Widmark formula accounts for body water distribution using a volume-of-distribution constant (r): males distribute alcohol across a larger proportion of body water (r = 0.73) than females (r = 0.66), resulting in higher BAC in women for the same dose. The liver metabolizes approximately 0.015% BAC per hour, regardless of coffee intake, cold showers, or exercise.

0.015%/hr
Liver metabolism rate
0.08%
US Legal Limit (DUI)
0.05%
EU Legal Limit
0.40%
Potentially Fatal Level

BAC Impairment Stages

0.00%–0.05%
  • 0.00–0.02%: No impairment detectable
  • 0.02–0.05%: Subtle mood changes, mild relaxation, slight motor impairment
  • Visual tracking begins to deteriorate at 0.04%
0.10%–0.30%+
  • 0.10–0.20%: Significant motor impairment, slurred speech, emotional instability
  • 0.20–0.30%: Severe impairment, blackout risk
  • >0.30%: Loss of consciousness, respiratory depression risk

Tolerance, Addiction & Long-Term Metabolic Effects

Regular alcohol consumption induces hepatic enzyme upregulation — particularly CYP2E1 — which increases alcohol metabolism rate in chronic drinkers. This creates the false impression that heavy drinkers are "less affected" at the same BAC, while simultaneously increasing their risk of acetaldehyde toxicity, hepatic inflammation, and cancer. The International Agency for Research on Cancer (IARC) classifies alcohol as a Group 1 carcinogen, causally linked to cancers of the oral cavity, pharynx, larynx, esophagus, liver, colon, rectum, and female breast.

The NIAAA defines heavy drinking as >4 drinks/day or >14 drinks/week for men, and >3 drinks/day or >7 drinks/week for women. Binge drinking is defined as a BAC ≥0.08% within 2 hours — typically 4 drinks for women or 5 drinks for men in that timeframe. Alcohol use disorder (AUD) affects approximately 14.5 million Americans, with neuroadaptation to alcohol's GABA-A potentiation leading to withdrawal syndromes ranging from anxiety and tremor to life-threatening delirium tremens at BAC 0.00% in dependent individuals.

10Clinical Reference: Normal Lab Values & Vital Signs

Quick-reference table for the most commonly assessed clinical parameters in adult outpatient and inpatient settings. Values may vary slightly by laboratory reference range and patient population.

Normal Adult Lab Values (Common):
Serum Creatinine: 0.7–1.2 mg/dL (male), 0.5–1.0 mg/dL (female) • Sodium: 135–145 mEq/L • Potassium: 3.5–5.0 mEq/L • eGFR: ≥60 mL/min/1.73m² • Hemoglobin: 13.5–17.5 g/dL (male), 12.0–15.5 g/dL (female) • QTc: <440 ms (male), <450 ms (female) • BMI: 18.5–24.9 kg/m²
Normal Adult Vital Signs:
Temperature: 36.1–37.2 °C (97–99 °F) • Heart Rate: 60–100 bpm • Respiratory Rate: 12–20 breaths/min • Blood Pressure: <120/<80 mmHg • O2 Saturation: ≥95% • MAP: 70–100 mmHg
60–100
Normal HR (bpm)
<120/80
Normal BP (mmHg)
≥60
Normal eGFR
≥95%
Normal SpO2

Key Diagnostic Cutoffs Quick Reference

Cardiometabolic Thresholds
  • Hypertension: ≥130/80 mmHg (AHA 2017)
  • Diabetes: FPG ≥126 mg/dL or HbA1c ≥6.5%
  • Prediabetes: FPG 100–125 or HbA1c 5.7–6.4%
  • LDL target: <70 mg/dL (high CV risk)
  • Triglycerides borderline: 150–199 mg/dL
  • eGFR CKD threshold: <60 for ≥3 months
Cardiac & Rhythm Values
  • Normal QTc male: <440 ms
  • Normal QTc female: <450 ms
  • Critical QTc: >500 ms (TdP risk)
  • Normal PR interval: 120–200 ms
  • Normal QRS: <120 ms
  • Normal HR: 60–100 bpm

11Medical Disclaimer & Clinical Methodology

All calculators on this page implement peer-reviewed, published clinical formulas and are intended for educational and reference purposes only. They do not constitute medical advice, diagnosis, or treatment. Never rely solely on a web-based calculator for clinical decision-making.

Important: Always verify calculated values with your institution's clinical decision support tools, a licensed pharmacist, or supervising physician. Patient-specific factors including comorbidities, concurrent medications, and individual pharmacokinetic variation may alter recommended thresholds significantly.

Formula Sources & Evidence Base

  • eGFR: Inker LA et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. NEJM 2021.
  • BMI: WHO Global Database on BMI. WHO Expert Consultation, 2004.
  • BMR: Mifflin MD et al. A new predictive equation for resting energy expenditure. Am J Clin Nutr 1990.
  • BSA: Mosteller RD. Simplified Calculation of Body-Surface Area. NEJM 1987.
  • QTc: Bazett HC. An analysis of the time-relations of electrocardiograms. Heart 1920.
  • Pregnancy: ACOG Practice Bulletin. Weight Gain During Pregnancy. 2013 reaffirmed 2020.
  • BAC: Widmark EMP. Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung. 1932.

12 Frequently Asked Questions

What is a normal BMI for adults?
A BMI between 18.5 and 24.9 is considered normal weight by the World Health Organization. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese. However, BMI does not differentiate between muscle and fat mass, so athletes may show elevated BMI despite very low body fat percentages.
How is eGFR calculated using the CKD-EPI 2021 formula?
The 2021 CKD-EPI race-free equation uses serum creatinine (Scr), age, and sex: eGFR = 142 × min(Scr/κ,1)^α × max(Scr/κ,1)^(−1.200) × 0.9938^Age × (1.012 if female). κ is 0.7 for females and 0.9 for males; α is −0.241 (female) or −0.302 (male). An eGFR ≥90 is Stage G1 (normal), while <15 is Stage G5 (kidney failure).
What QTc value is considered dangerously prolonged?
A QTc above 500 ms carries significant risk of torsades de pointes, a potentially fatal arrhythmia. QTc 440–500 ms in men (or 450–500 ms in women) is considered borderline prolonged and warrants medication review. Bazett's formula (QTc = QT/√RR) is most widely used clinically.
How does the Widmark formula calculate BAC?
BAC = (alcohol grams × 100) / (weight_lbs × r × 453.592) − (0.015 × hours elapsed), where r = 0.73 for males and 0.66 for females. Each standard drink contains approximately 14g of pure alcohol. The liver metabolizes approximately 0.015% BAC per hour on average regardless of food, coffee, or water intake.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the energy your body needs at complete rest to sustain vital functions — breathing, circulation, cell production. TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (extremely active). The Mifflin-St Jeor equation is the most validated formula for BMR estimation in modern populations.
Which BSA formula is used for chemotherapy dosing?
The Mosteller formula (BSA = √[height_cm × weight_kg / 3600]) is the most commonly used in oncology for its simplicity and good validation. The DuBois formula (0.007184 × H^0.725 × W^0.425) was historically standard. Haycock's formula is preferred for pediatric patients due to its specific validation in children and neonates.
How is the due date calculated from LMP?
Naegele's rule adds 280 days (40 weeks) to the first day of the last menstrual period, assuming a 28-day cycle. For longer cycles, add the extra days to the EDD. For example, a 32-day cycle gives EDD = LMP + 284 days. Ultrasound dating between 8–13+6 weeks is more accurate than LMP dating when there is a discrepancy of more than 5–7 days.
What are the CKD stages and what actions do they require?
CKD stages by eGFR: G1 (≥90, normal – treat underlying disease), G2 (60–89, mildly decreased – annual monitoring), G3a (45–59, mild-moderate – 6-month monitoring, diet consult), G3b (30–44, moderate-severe – nephrology referral recommended), G4 (15–29, severely decreased – urgent nephrology, RRT planning), G5 (<15, kidney failure – dialysis or transplant). All stages also incorporate albuminuria categories A1, A2, A3.
What is MAP and why does it matter?
Mean Arterial Pressure (MAP) = DBP + (SBP − DBP)/3. A MAP of 65–70 mmHg or higher is generally required to perfuse the brain, kidneys, and heart. In ICU settings, target MAP for septic shock is ≥65 mmHg. MAP below 60 mmHg is a clinical emergency indicating potential organ failure.
What is the IOM recommendation for pregnancy weight gain?
The 2009 Institute of Medicine guidelines recommend: Underweight (BMI <18.5): 12.5–18 kg; Normal weight (18.5–24.9): 11.5–16 kg; Overweight (25–29.9): 7–11.5 kg; Obese (BMI ≥30): 5–9 kg total gain during pregnancy. Twin pregnancies have substantially higher recommended ranges for all BMI categories.
How do drop factors affect IV drip rate calculation?
Drip rate (gtts/min) = Volume (mL) × Drop Factor / Time (min). Standard macro-drip sets use 10, 15, or 20 drops/mL. Micro-drip (pediatric) sets use 60 drops/mL. Example: 500 mL over 4 hours with 20 gtt/mL = 500×20/(4×60) = 41.7, rounded to 42 drops/min. For infusion pumps: simply Volume ÷ Time in hours = mL/hr.
How long does it take to sober up?
The liver processes approximately 0.015% BAC per hour — roughly one standard drink per hour on average. A person with 0.10% BAC needs about 6–7 hours to reach 0.00%. Coffee, cold showers, food, and exercise do not accelerate alcohol metabolism — only time eliminates alcohol from the bloodstream.
Can I use adult BMI categories for children?
No. For children and adolescents aged 2–19, BMI-for-age percentile charts (CDC or WHO) are used rather than fixed cutoffs. A BMI at or above the 95th percentile is obese; 85th–94th is overweight; 5th–84th is healthy weight; below 5th is underweight. Adult BMI thresholds (18.5, 25, 30) do not apply to pediatric populations.
Is an IV drip rate calculator safe for clinical use?
Online calculators provide educational guidance and serve as a double-check mechanism. Always verify calculations at the bedside with a registered nurse or clinical pharmacist. For high-risk medications such as heparin, potassium chloride, or insulin, institutional protocols and infusion pumps with dose-error reduction software (DERS) are mandatory and should not be bypassed.
What is the normal BSA for an adult?
The average BSA for adult men is approximately 1.9 m² and for adult women approximately 1.6 m². The reference BSA of 1.73 m² is used as the standard for normalizing GFR (reported as mL/min/1.73m²). Chemotherapy doses are calculated per m² of BSA to account for metabolic variability between patients of different sizes.

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