Health Calculators

Free, evidence-based medical calculators to help you understand your health metrics

Important: These calculators are for educational purposes only and should not replace professional medical advice. Always consult with a healthcare provider before making any health decisions based on these results. The formulas used are standard medical calculations but may not account for all individual factors.

Body Mass Index (BMI)

BMI is a widely used screening tool that estimates body fat based on height and weight. While it doesn't measure body fat directly, it correlates with more direct measures and helps identify potential weight-related health risks.

kg/m²

BMI Categories (Adults):

  • < 18.5: Underweight
  • 18.5 - 24.9: Normal weight
  • 25.0 - 29.9: Overweight
  • 30.0 - 34.9: Obesity Class I
  • 35.0 - 39.9: Obesity Class II
  • ≥ 40.0: Obesity Class III

Body Surface Area (BSA)

BSA is used in clinical settings to calculate drug dosages, assess kidney function, and determine cardiac index. The Mosteller formula is one of the most commonly used methods for its simplicity and accuracy.

m² (Mosteller Formula)

Typical BSA Ranges:

  • Average adult male: 1.7 - 2.0 m²
  • Average adult female: 1.5 - 1.8 m²
  • Newborn: ~0.25 m²
  • Child (10 years): ~1.1 m²

Mean Arterial Pressure (MAP)

MAP represents the average blood pressure during a single cardiac cycle and indicates how well blood is flowing to vital organs. It's a critical value in clinical settings for assessing organ perfusion.

mmHg

MAP Interpretation:

  • < 60 mmHg: Inadequate organ perfusion (critical)
  • 65-70 mmHg: Minimum for organ perfusion
  • 70-100 mmHg: Normal range
  • > 100 mmHg: Elevated (may indicate hypertension)

Creatinine Clearance (Cockcroft-Gault)

This equation estimates kidney function (GFR) using serum creatinine, age, weight, and sex. It's commonly used to adjust medication dosages in patients with impaired kidney function.

mL/min

Kidney Function Stages:

  • ≥ 90: Normal kidney function
  • 60-89: Mildly decreased (CKD Stage 2)
  • 45-59: Mild-moderate decrease (CKD Stage 3a)
  • 30-44: Moderate-severe decrease (CKD Stage 3b)
  • 15-29: Severely decreased (CKD Stage 4)
  • < 15: Kidney failure (CKD Stage 5)

Corrected QT Interval (QTc)

The QTc adjusts the QT interval for heart rate, making it comparable across different rates. Prolonged QTc can indicate risk for dangerous arrhythmias. Uses Bazett's formula (most common).

ms (Bazett's Formula)

QTc Ranges:

  • Normal (males): < 450 ms
  • Normal (females): < 460 ms
  • Borderline: 450-470 ms (males), 460-480 ms (females)
  • Prolonged: > 470 ms (males), > 480 ms (females)
  • High risk for TdP: > 500 ms

Calcium Correction for Hypoalbuminemia

Approximately 40% of serum calcium is bound to albumin. When albumin levels are low, total calcium appears falsely low. This formula adjusts calcium to reflect what it would be with normal albumin.

mg/dL (Corrected)

Calcium Reference Ranges:

  • Low (Hypocalcemia): < 8.5 mg/dL
  • Normal: 8.5 - 10.5 mg/dL
  • High (Hypercalcemia): > 10.5 mg/dL
  • Critical high: > 12.0 mg/dL

CHA₂DS₂-VASc Score

This scoring system estimates stroke risk in patients with atrial fibrillation. It helps guide decisions about anticoagulation therapy to prevent thromboembolic events.

CHA₂DS₂-VASc Score

Score Interpretation & Annual Stroke Risk:

  • 0 (males): Low risk (~0%), no anticoagulation
  • 1: Low-moderate (~1.3%), consider anticoagulation
  • 2: Moderate (~2.2%), anticoagulation recommended
  • 3: Moderate-high (~3.2%)
  • 4-9: High risk (4-15%+)

Wells' Criteria for Pulmonary Embolism

This clinical decision rule helps assess the probability of pulmonary embolism (PE) before ordering diagnostic tests. It guides whether D-dimer testing or imaging is appropriate.

Wells' Score

Risk Stratification:

  • Low (< 2): ~1.3% PE probability
  • Moderate (2-6): ~16.2% PE probability
  • High (> 6): ~37.5% PE probability
  • PE Unlikely (≤ 4): D-dimer can rule out
  • PE Likely (> 4): Consider imaging

Fibrosis-4 (FIB-4) Index

FIB-4 is a non-invasive tool to estimate liver fibrosis in patients with hepatitis or fatty liver disease. It helps determine if further evaluation (like elastography or biopsy) is needed.

FIB-4 Index

FIB-4 Interpretation (Age < 65):

  • < 1.30: Low risk - advanced fibrosis excluded (NPV 90%)
  • 1.30 - 2.67: Intermediate - further evaluation needed
  • > 2.67: High risk - advanced fibrosis likely (PPV 80%)

Note: For age ≥ 65, use cut-offs of <2.0 and >2.67

Target Heart Rate Zones

Knowing your target heart rate zones helps optimize workout intensity. These zones are based on your maximum heart rate (220 - age) and help you train effectively for different fitness goals.

Estimated Max Heart Rate

Heart Rate Zones:

  • Zone 1 (50-60%): Recovery, warm-up
  • Zone 2 (60-70%): Fat burning, endurance base
  • Zone 3 (70-80%): Aerobic, cardiovascular fitness
  • Zone 4 (80-90%): Anaerobic threshold, performance
  • Zone 5 (90-100%): Maximum effort, VO2 max