Health Calculators

Start From the Question, Not the Tool

Tool names are not always obvious about what they answer, particularly on the clinical side where two calculators can sound almost identical. This is the shortest route from a question to the right page.

The Everyday Three Answer Different Questions

BMI, body fat and calories are often treated as interchangeable health metrics. They are not, and using only one of them is where most confusion comes from.

BMI compares weight against height and nothing else. It is fast and it is a screening figure — useful for placing yourself roughly, useless for telling muscle from fat. Body fat percentage adds the dimension BMI is missing by using tape measurements to estimate composition, which is why two people with identical BMI can produce very different body fat results. Calorie needs answer a third question entirely: not what your body is made of, but how much energy it uses.

A sensible sequence is BMI first for a rough position, body fat second if the BMI result seems at odds with how you look, and calories third once you have decided whether you want the number to change.

The Clinical Five Sit in a Chain

The clinical calculators are not alternatives to each other. Each handles one link between a prescription and an administered dose, and a single order can pass through three of them.

Prescription in mg/kg
→ Dosage calculator gives the dose in mg
→ Dose stock calculator converts mg into tablets or mL
→ IV calculator turns that into a pump rate or drip rate

A paediatric antibiotic order typically stops after the second step. An intravenous antibiotic runs the full chain. An immunoglobulin infusion adds a fourth consideration, since the rate changes during administration rather than staying fixed.

The two pharmacology calculators sit alongside rather than inside that chain. Pharmacokinetics answers what the body does to the drug — half-life, clearance, how long until a level is meaningful. Pharmacodynamics answers what the drug does to the body once it arrives. Both are more often used for study and for interpreting monitored levels than at the point of administration.

What These Tools Do Not Do

Every calculator here checks arithmetic. None of them checks clinical judgement, and the difference matters most on the pages where the stakes are highest.

A dose calculator cannot know the drug, the indication, the patient's renal function, what else they are taking, or whether the rate you typed was the one on the prescription. It will multiply whatever it is given and return a confident-looking number. Treat every clinical result as a figure to be checked against the prescribing reference, and for high-risk medicines, recalculated independently by a second clinician rather than confirmed by them.

The consumer tools carry a milder version of the same limit. They apply population equations to your measurements, which makes them a good starting estimate and a poor final verdict. Each page sets out where its own method breaks down.

How These Pages Are Reviewed

The clinical formulas, dosing logic, unit handling and safety wording across these calculators were reviewed for accuracy by Dr. Syeda Khadija Akbar, PharmD, our medical reviewer. Each page shows its own review date, and the disclaimer sets out what that review does and does not cover.