99 clinical calculators, free.
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Anaesthesia 5
Apfel Simplified PONV Risk Score
Estimates risk of postoperative nausea and vomiting from 4 simple risk factors, to guide antiemetic prophylaxis intensity.
ARISCAT Score
Predicts risk of postoperative pulmonary complications from 7 preoperative and surgical factors.
ASA Physical Status Classification
Standardized preoperative assessment of a patient's overall health, used across anesthesiology and surgery for risk communication and case planning.
Lean Body Weight (LBW)
Estimates fat-free body weight — the Boer formula is shown as primary (a widely-used modern clinical reference), with James shown alongside since the two formulas can diverge meaningfully, especially at higher BMI.
Mallampati Score
Visual airway assessment (mouth open, tongue protruded, sitting upright, not phonating) used to help predict difficulty of laryngoscopy/intubation.
Cardiology 10
CHA₂DS₂-VASc Score
Estimates annual stroke risk in atrial fibrillation to guide the anticoagulation decision.
Corrected QT Interval (QTc)
Heart-rate-corrected QT interval, shown by both the Bazett and Fridericia formulas.
GRACE Score (ACS In-Hospital Mortality)
Estimates in-hospital mortality risk in acute coronary syndrome from 8 clinical variables — one of two guideline-endorsed risk scores for ACS (alongside TIMI).
HAS-BLED Score
Estimates 1-year major bleeding risk in patients on anticoagulation for atrial fibrillation.
HEART Score
Risk-stratifies emergency department chest pain patients for 6-week major adverse cardiac events (MACE).
PERC Rule
Rules out pulmonary embolism without further testing in patients already judged low pretest probability — only valid when applied to that population.
Revised Cardiac Risk Index (RCRI)
Estimates perioperative cardiac risk before noncardiac surgery from six independent risk factors.
TIMI Risk Score (UA/NSTEMI)
Estimates 14-day risk of death, MI, or urgent revascularization in unstable angina/NSTEMI. Distinct from the separate TIMI STEMI score, which is not this tool.
Wells' Criteria for DVT
Estimates pretest probability of deep vein thrombosis to guide D-dimer testing versus direct ultrasound.
Wells' Criteria for Pulmonary Embolism
Estimates pretest probability of pulmonary embolism to guide D-dimer testing versus direct imaging.
Critical care 7
APACHE II Score
Severity-of-disease classification for adult ICU patients, from 12 physiologic variables plus age and chronic health status, within the first 24 hours of admission.
Glasgow Coma Scale (GCS)
Standardized assessment of level of consciousness — eye, verbal, and motor response.
NEWS2 (National Early Warning Score 2)
Bedside score for detecting clinical deterioration on the general ward, from six routinely-measured vital signs.
qSOFA (Quick SOFA)
Bedside screen for patients with suspected infection who are at risk of a poor outcome from sepsis — no labs required.
Richmond Agitation-Sedation Scale (RASS)
Standardized bedside assessment of sedation depth and agitation level in ICU patients.
Shock Index
Rapid bedside marker of hemodynamic compromise — heart rate divided by systolic blood pressure.
SOFA (Sequential Organ Failure Assessment)
Full six-organ-system severity score used to track organ dysfunction over an ICU stay and, per Sepsis-3, to define sepsis (acute rise ≥2 from baseline with suspected infection).
Dermatology 4
Fitzpatrick Skin Type
Classifies skin's characteristic response to UV exposure — used to select safe laser/light-based device settings and peel depths.
Hurley Stage (Hidradenitis Suppurativa)
Classifies hidradenitis suppurativa severity into 3 stages, guiding treatment intensity.
NAPSI (Nail Psoriasis Severity Index)
Quantifies nail psoriasis severity in a single nail, from four nail-matrix and four nail-bed features.
Rule of Nines (Burn %TBSA, Adult)
Rapid estimate of total body surface area burned in adults, for fluid resuscitation and referral decisions.
Emergency medicine 1
Endocrinology 5
Basal Metabolic Rate (BMR)
Estimates resting daily energy expenditure — the Mifflin-St Jeor equation (generally the more accurate modern default), shown alongside the classic Harris-Benedict equation for reference.
Daily Calorie Requirement
Estimates total daily energy expenditure (TDEE) from BMR (Mifflin-St Jeor) and an activity level multiplier.
HbA1c to Estimated Average Glucose (eAG)
Converts HbA1c into an estimated average glucose, in the same units patients see on a glucose meter — often more intuitive for patient counseling.
HOMA-B
Estimates pancreatic beta-cell function (insulin secretory capacity) from fasting glucose and insulin, alongside HOMA-IR.
QUICKI
Quantitative Insulin Sensitivity Check Index — an alternative to HOMA-IR for estimating insulin sensitivity from fasting glucose and insulin.
General 9
Adjusted Body Weight
Adjusts ideal body weight upward for obese patients — used for dosing drugs where actual body weight overestimates the effective dose.
Anion Gap
Screens for the cause of a metabolic acidosis by identifying unmeasured anions.
Body Mass Index (BMI)
Screens for underweight, overweight, and obesity from height and weight.
Body Surface Area (Mosteller)
Body surface area from height and weight — used for chemotherapy dosing, cardiac index, and burn calculations.
Calcium Correction for Hypoalbuminemia
Adjusts total serum calcium for low albumin, since ~40% of calcium is albumin-bound.
HOMA-IR
Estimates insulin resistance from fasting glucose and fasting insulin — a research/screening tool, not a diagnostic test for diabetes.
Ideal Body Weight (Devine)
Devine formula for ideal body weight — commonly used as the basis for weight-based drug dosing.
Serum Osmolality (Calculated)
Estimates serum osmolality from routine labs — compare against a measured (lab) osmolality to screen for an osmolar gap (e.g. toxic alcohol ingestion).
Sodium Correction for Hyperglycemia
Adjusts measured sodium for hyperglycemia-driven osmotic dilution — the classic Katz correction factor.
Haematology 5
4Ts Score
Pretest probability of heparin-induced thrombocytopenia (HIT) from four clinical criteria — its main value is a low score's ability to rule HIT out.
Absolute Neutrophil Count (ANC)
Quantifies neutropenia severity from a WBC count and differential.
Caprini Score (2005)
Estimates postoperative venous thromboembolism (VTE) risk to guide prophylaxis choice — the widely-used 2005 version.
Corrected Reticulocyte Index
Adjusts the reticulocyte percentage for the degree of anemia and reticulocyte maturation time, to assess whether the bone marrow response to anemia is adequate.
Khorana Score
Predicts risk of chemotherapy-associated venous thromboembolism in ambulatory cancer patients, to guide consideration of primary thromboprophylaxis.
Hepatology 4
APRI (AST to Platelet Ratio Index)
Simple noninvasive index for significant fibrosis/cirrhosis, using only AST and platelet count.
Child-Pugh Score
Grades cirrhosis severity and estimates surgical/prognostic risk from five clinical and laboratory criteria.
FIB-4 Index
Noninvasive estimate of liver fibrosis from age and routine labs — a first-line screen before considering elastography or biopsy.
MELD-Na Score
Predicts 90-day mortality in advanced liver disease — the OPTN/UNOS 2016 score used for liver transplant allocation.
Infectious diseases 2
Neurology 5
ABCD² Score
Estimates short-term (2-day and 7-day) stroke risk after a suspected TIA.
Hunt and Hess Grade
Grades clinical severity of aneurysmal subarachnoid hemorrhage, used for prognosis and surgical timing decisions.
ICH Score
Predicts 30-day mortality after spontaneous intracerebral hemorrhage from five clinical/radiological findings.
Modified Rankin Scale (mRS)
Measures the degree of disability or dependence after stroke or other neurological disability.
NIH Stroke Scale (NIHSS)
Standardized 15-item neurological exam quantifying stroke severity — used for eligibility screening and serial monitoring after thrombolysis/thrombectomy.
Obstetrics 5
Bishop Score
Assesses cervical readiness for labor induction from a bimanual exam — higher scores predict a higher chance of successful vaginal delivery after induction.
Estimated Due Date (Naegele's Rule)
Estimates the due date from the first day of the last menstrual period, assuming a regular 28-day cycle.
Gestational Age by LMP
Current gestational age in weeks and days, from the last menstrual period, as of today.
Pre-Pregnancy BMI
BMI calculated from pre-pregnancy (or first-trimester) weight — the basis for IOM gestational weight gain targets.
Pregnancy Weight Gain (IOM Guidelines)
Recommended total gestational weight gain for a singleton pregnancy, by pre-pregnancy BMI category (Institute of Medicine 2009 guidelines).
Oncology 2
ECOG Performance Status
Standardized measure of a cancer patient's functional status — widely used to guide chemotherapy eligibility and trial enrollment.
Karnofsky Performance Scale (KPS)
Rates a patient's functional capacity in 10-point increments from 0 (dead) to 100 (normal) — an older but still widely-used alternative to ECOG.
Ophthalmology 4
Astigmatism Vector Combination
Combines two cylindrical (astigmatic) powers at different axes into a single resultant cylinder and axis — e.g. combining corneal astigmatism with a surgically-induced astigmatism vector.
Spherical Equivalent
Converts a spherocylindrical refraction into a single equivalent spherical power.
Vertex Distance Conversion
Converts a spectacle lens power at one vertex distance to the equivalent power at another (e.g. spectacle plane to corneal plane) — most clinically relevant for powers beyond about ±4D.
Visual Acuity Conversion (Snellen ↔ LogMAR)
Converts between Snellen fraction and LogMAR notation — LogMAR is preferred for research/statistical analysis because it has equal-sized steps across the acuity range.
Orthopaedics 3
Mangled Extremity Severity Score (MESS)
Predicts likelihood of eventual amputation in a severely injured limb, to help guide the salvage-versus-amputation decision.
Ottawa Ankle Rules
Decides whether an ankle X-ray is needed after acute ankle injury.
Ottawa Knee Rules
Decides whether a knee X-ray is needed after acute knee injury.
Paediatrics 3
APGAR Score
Standardized newborn assessment at 1 and 5 minutes after birth.
Corrected Age (Premature Infant)
Adjusts a premature infant's chronological age for degree of prematurity — used for growth and developmental-milestone assessment, typically until 2 years chronological age.
Pediatric Weight Estimation
Estimates a child's weight from age using the APLS formula, for use when an actual weight isn't available — with the matching Broselow tape color zone shown for equipment-sizing reference.
Psychiatry 2
Pulmonology 7
Alveolar-Arterial (A-a) Gradient
Distinguishes hypoxemia from impaired gas exchange (elevated gradient) versus hypoventilation alone (normal gradient).
Arterial Oxygen Content (CaO₂)
Total oxygen carried in arterial blood — the basis for calculating oxygen delivery (DO₂) alongside cardiac output.
CURB-65 Pneumonia Severity
Estimates community-acquired pneumonia severity and mortality risk to guide the inpatient-vs-outpatient decision.
Modified Medical Research Council (mMRC) Dyspnea Scale
Grades the functional impact of breathlessness — used in COPD severity assessment (e.g. the ABCD/GOLD assessment tool).
PaO₂/FiO₂ Ratio (P/F Ratio)
Quantifies the severity of hypoxemia and, per the Berlin Definition, classifies ARDS severity.
ROX Index
Predicts high-flow nasal cannula (HFNC) failure/need for intubation in acute hypoxemic respiratory failure.
STOP-BANG
Screens for obstructive sleep apnea risk from 8 yes/no criteria — commonly used preoperatively.
Renal 6
Creatinine Clearance (Cockcroft-Gault)
Estimates creatinine clearance for renal drug-dosing decisions — still the reference standard for many drug labels' dosing tables, even where eGFR is preferred for CKD staging.
eGFR (CKD-EPI 2021, Race-Free)
Estimates glomerular filtration rate for CKD staging — the 2021 race-free creatinine equation, now the recommended standard (National Kidney Foundation / ASN Task Force).
Fractional Excretion of Sodium (FENa)
Distinguishes prerenal azotemia from intrinsic renal causes (e.g. ATN) in acute kidney injury.
Fractional Excretion of Urea (FEUrea)
Alternative to FENa for distinguishing prerenal azotemia from intrinsic renal injury — useful specifically when the patient is on diuretics, which make FENa unreliable.
Free Water Deficit
Estimates the free water deficit in hypernatremia, to guide the volume of water/hypotonic fluid replacement.
Urine Protein-to-Creatinine Ratio
Estimates 24-hour urinary protein excretion from a single spot urine sample, avoiding the need for a timed collection.
Rheumatology 5
BASDAI
Bath Ankylosing Spondylitis Disease Activity Index — a patient-reported measure of axial spondyloarthritis symptom severity.
BASFI
Bath Ankylosing Spondylitis Functional Index — a patient-reported measure of functional limitation.
Clinical Disease Activity Index (CDAI)
Rheumatoid arthritis disease activity from joint counts and global assessments — no lab values needed, so it can be scored the same day.
Modified Health Assessment Questionnaire (mHAQ)
Abbreviated 8-item version of the Health Assessment Questionnaire, measuring functional disability in daily activities.
Simplified Disease Activity Index (SDAI)
Rheumatoid arthritis disease activity — CDAI plus CRP.
Surgery and GI 5
Alvarado Score
Clinical prediction score for acute appendicitis, combining symptoms, signs, and basic labs (MANTRELS).
BISAP Score
Predicts mortality risk in acute pancreatitis within the first 24 hours, from 5 simple criteria.
Glasgow-Blatchford Score
Risk-stratifies upper GI bleeding at first contact — a score of 0 identifies patients who may be safe for outpatient management.
Maddrey Discriminant Function
Assesses severity of alcoholic hepatitis and identifies patients who may benefit from corticosteroid therapy.
Surgical Apgar Score
Estimates risk of major postoperative complications from three intraoperative measurements — estimated blood loss, lowest MAP, and lowest heart rate.
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