Medical calculators
38 calculators, with the formula shown.
Every page gives the result, the band it falls in, the formula written out, a worked example, when the calculation does not apply, and the paper it comes from. Free, no account, and nothing you type leaves your browser.
General and clinical
The everyday bedside calculations: body size, perfusion, consciousness and electrolytes.
BMI calculator
Body mass index is weight divided by height squared, and it places a person in a weight band. This calculator shows both the WHO international bands and the lower Asian-Indian cut-offs, because they disagree and the Indian ones are the relevant pair here.
Body surface area (BSA)
Body surface area estimates the area of a person’s skin from height and weight. It is the basis for chemotherapy dosing, some pediatric dosing, and cardiac index.
Mean arterial pressure (MAP)
Mean arterial pressure is the average pressure driving blood into the tissues over one cardiac cycle. It is the number resuscitation targets are written against, rather than the systolic.
Glasgow Coma Scale (GCS)
The Glasgow Coma Scale scores eye, verbal and motor responses to describe a person’s level of consciousness in one number between 3 and 15. It is recorded as three components, not just a total.
Anion gap
The anion gap is the difference between measured cations and measured anions, and it separates the causes of a metabolic acidosis into two groups. Correcting it for albumin matters, because a low albumin hides a raised gap.
Corrected calcium
About half of serum calcium is bound to albumin, so a low albumin makes total calcium look low when the free, active fraction is normal. This adjusts the measured value for the albumin.
Sodium correction for hyperglycemia
A high glucose pulls water into the vascular space and dilutes sodium, so the measured sodium understates the true value. This gives the sodium you would expect once the glucose is normal.
Cardiology
Stroke and bleeding risk in atrial fibrillation, QT correction, acute coronary and perioperative risk.
CHA₂DS₂-VASc score
CHA₂DS₂-VASc estimates yearly stroke risk in a person with non-valvular atrial fibrillation, and is the score anticoagulation decisions are written against. Age 75 or over and a prior stroke score two points; everything else scores one.
HAS-BLED score
HAS-BLED estimates major bleeding risk in a person on anticoagulation for atrial fibrillation. Its purpose is to find modifiable risk factors, not to withhold anticoagulation.
Corrected QT interval (QTc)
QTc adjusts the measured QT interval for heart rate so it can be compared against a threshold. A prolonged QTc raises the risk of torsades de pointes, which is why it is checked before and during QT-prolonging drugs.
TIMI risk score (UA/NSTEMI)
The TIMI risk score estimates 14-day risk of death, myocardial infarction or urgent revascularization in unstable angina or NSTEMI. Seven equally weighted criteria, scored on arrival.
Framingham 10-year cardiovascular risk
This estimates the chance of a first cardiovascular event, whether coronary, cerebrovascular, peripheral arterial or heart failure, in the next ten years, from the 2008 general Framingham risk profile. It is an estimate for a person without established cardiovascular disease.
Revised Cardiac Risk Index (RCRI)
The RCRI estimates the risk of a major cardiac event after non-cardiac surgery from six equally weighted clinical factors. It is the starting point of most preoperative cardiac assessments.
Renal
Kidney function for staging and for drug dosing, and the acute kidney injury work-up.
Creatinine clearance (Cockcroft-Gault)
Cockcroft-Gault estimates creatinine clearance from age, weight, sex and serum creatinine. It is the equation most drug labels are written against, which is why it survives alongside eGFR.
eGFR (CKD-EPI 2021)
Estimated glomerular filtration rate places kidney function on the CKD staging scale. The default here is the 2021 CKD-EPI creatinine equation, which removed the race coefficient the earlier version carried.
Fractional excretion of sodium (FENa)
FENa is the proportion of filtered sodium the kidney excretes, and it separates pre-renal acute kidney injury from intrinsic tubular injury. Under 1% suggests the kidney is holding on to sodium; over 2% suggests it cannot.
Pediatrics
Newborn assessment, weight-based dosing and reference weights for children.
APGAR score
The APGAR score describes a newborn’s condition at one and five minutes across five signs, each scored 0 to 2. It records how the baby is, and how the baby responds to whatever is being done. It does not predict outcome on its own.
Pediatric dose
This converts a milligrams-per-kilogram dose into a dose in milligrams and, for a syrup, a volume in milliliters. Every result is checked against the adult ceiling you supply, because weight-based dosing in an older child can exceed it.
Obstetrics
Dating a pregnancy, and assessing the cervix before induction.
Pregnancy due date (EDD)
This estimates the expected date of delivery from the last menstrual period, from a dating ultrasound, or from a known conception date. Where an early scan disagrees materially with the dates, the scan is what obstetric practice uses.
Gestational age
This gives the current gestation in completed weeks and days, from either the last menstrual period or a known due date. It is the number every antenatal decision is indexed against.
Emergency and critical care
Pretest probability, sepsis screening, organ failure, stroke severity, trauma and burns.
Wells score (DVT and PE)
The Wells score turns clinical findings into a pretest probability of deep vein thrombosis or pulmonary embolism, which is what decides whether a D-dimer or imaging comes next. Pick the version you need, because the two have different items and different weights.
qSOFA
qSOFA is a three-item bedside screen that flags a patient with suspected infection who is at higher risk of a poor outcome. It needs no blood test, which is the whole point of it.
Alvarado score
The Alvarado score combines symptoms, signs and two laboratory findings into a likelihood of acute appendicitis. It is best used to identify the patient who does not need imaging and the one who probably does.
Ottawa ankle and knee rules
The Ottawa rules decide whether an X-ray is needed after an ankle, midfoot or knee injury. They are highly sensitive for clinically significant fracture, which is what makes a negative result safe to act on.
Infectious disease
Pneumonia severity and the sore-throat antibiotic decision.
CURB-65
CURB-65 grades the severity of community-acquired pneumonia and indicates where the patient should be treated. Five criteria, one point each, and the score maps to 30-day mortality.
Centor score (McIsaac modified)
The Centor score estimates how likely a sore throat is to be streptococcal, and therefore whether testing or an antibiotic is warranted. The McIsaac modification adds an age adjustment, which matters in a pediatric population.
Pulmonology
Oxygenation and the pulmonary embolism rule-out.
Alveolar-arterial (A-a) gradient
The A-a gradient is the difference between the oxygen in the alveolus and the oxygen in the artery, and it separates causes of hypoxemia. A normal gradient points at hypoventilation or altitude; a raised one at shunt, V/Q mismatch or a diffusion problem.
PERC rule
The Pulmonary Embolism Rule-out Criteria are eight findings that, when all are absent in a patient already judged low risk, make PE unlikely enough that no further testing is needed. It is a rule-out, and only for low-risk patients.
Diabetes and metabolic
Translating HbA1c, and estimating insulin resistance.
HbA1c to average glucose
HbA1c reflects average blood glucose over roughly the last three months. This converts the percentage into an average glucose, which is the number most patients can actually picture.
HOMA-IR
HOMA-IR estimates insulin resistance from a single pair of fasting insulin and fasting glucose values. It is a research and screening index rather than a diagnostic test.
Nutrition
Reference weights and energy requirements.
Ideal body weight
Ideal body weight is a reference weight derived from height and sex, used for dosing and for ventilator tidal volumes. Adjusted body weight, shown alongside, is what several drug protocols actually ask for in obesity.
Daily caloric needs
This estimates resting energy expenditure and then total daily energy expenditure once activity is taken into account. It is a starting point for a nutrition plan, adjusted afterwards against what actually happens to the weight.
Fluids and dosing
Maintenance fluid, drip rates, and antimicrobial dosing by renal function.
Hepatology and coagulation
Severity of liver disease, and the INR.
Mental health
Validated screening instruments for depression, anxiety and cognition.
PHQ-9 depression scale
The PHQ-9 asks about the nine symptoms of depression over the last two weeks and scores each 0 to 3. It is a screening and severity tool, and it is also how change over time is measured once treatment starts.
GAD-7 anxiety scale
The GAD-7 asks about seven anxiety symptoms over the last two weeks. It screens for generalized anxiety disorder and performs reasonably as a screen for panic, social anxiety and post-traumatic stress as well.
India-specific
Instruments developed and validated for Indian practice, which imported scores do not replace.
Indian Diabetes Risk Score (MDRF-IDRS)
The MDRF Indian Diabetes Risk Score identifies people who should be screened for undiagnosed type 2 diabetes, using four questions and no blood test. It was developed and validated in an Indian population, which is why it is used here in preference to imported risk scores.
Modified Kuppuswamy socioeconomic scale
The Modified Kuppuswamy scale classifies an urban Indian family’s socioeconomic status from the head of the family’s education, occupation and total monthly family income. It is used constantly in Indian clinical research and in public health practice.
Use them with judgment.
This calculator is provided for reference and education. It does not replace clinical assessment, examination, current guidelines, local protocol, or professional judgment. Verify every result before acting on it. Nirogix accepts no liability for clinical decisions made using this tool.
Common questions
- Are these calculators free?
- Yes. Every calculator is free, needs no account, and has no usage limit. They exist because clinicians look for them, and because a calculator page makes no claim about our software that we would have to defend.
- Is anything I type stored or sent anywhere?
- No. Every calculation runs in your browser. Nothing is transmitted to us, nothing is stored, and there is no analytics on these pages watching what you enter.
- Can I rely on these for clinical decisions?
- They are reference calculations, not clinical decision support. Each page shows the formula, the population it was derived in, and the situations where it does not apply. Read those before acting on a number, and verify anything that matters.
- Why do some pages show both WHO and Indian cut-offs?
- Because they disagree, and for an Indian patient the Indian ones are usually the relevant pair. BMI is the clearest case: the Asian-Indian thresholds for overweight and obesity sit lower than the WHO international bands.
- Will these work inside the Nirogix Portal?
- That is planned. The same calculation engine is designed to run inside the consultation record, pre-filled from the chart, with the result and the inputs that produced it saved together. It is scheduled scope, not something you can use today.