Pharmacology Calculators
Free pharmacokinetics calculators: half-life, clearance, volume of distribution, bioavailability, AUC, and one-compartment models. Reference use only.
Pharmacology Calculators - Pharmacokinetics Math for Students and Clinicians
Pharmacokinetics describes what the body does to a drug: how it distributes into tissue, how fast it is eliminated, and how its concentration rises and falls over time after a dose. CalculatorPod’s pharmacology calculators apply the standard first-order kinetic equations used throughout pharmacy school, nursing school, and clinical pharmacology to compute half-life, elimination rate constants, volume of distribution, and related concentration-time relationships.
These calculators are for reference and educational purposes only. They are general pharmacokinetic math applied to the numbers you enter, they are not a diagnosis, a prescription, or a substitute for a licensed clinician or pharmacist. Never use any calculator on this page to determine an actual medication dose for yourself or anyone else. See our full Disclaimer for details.
Ten Pharmacology Calculators
Drug Half-Life Calculator - Finds a drug’s plasma half-life and elimination rate constant from two concentration measurements taken at different times, using first-order elimination kinetics with a decay-curve chart.
Elimination Rate Constant Calculator - Converts a known half-life into the elimination rate constant (ke), the percent eliminated per hour, and the percent remaining after any chosen elapsed time.
Volume of Distribution Calculator - Computes a drug’s apparent volume of distribution from an IV bolus dose and initial plasma concentration, with a per-kilogram value and a tissue-distribution classification.
Clearance Rate Calculator - Computes total body clearance from the elimination rate constant and volume of distribution, shown in both L/hr and mL/min, with an illustrative plasma decay chart.
Bioavailability and Oral Dose Adjustment Calculator - Finds absolute bioavailability from oral and IV AUC data, then the oral dose needed to match a target IV exposure.
AUC Calculator (Trapezoidal Method) - Calculates total drug exposure (area under the curve) from 5 timed plasma concentration readings using the standard linear trapezoidal method, with a segment-by-segment breakdown table.
One-Compartment IV Bolus Model Calculator - Models the full plasma concentration decay curve after an instantaneous IV bolus, C(t)=(Dose/Vd)e^(-ke t), at any time you choose.
One-Compartment IV Infusion Model Calculator - Models concentration during a continuous IV infusion approaching steady state, and the exponential decline once the infusion stops, with automatic phase detection.
One-Compartment Oral Dose Model Calculator - Models the rise-then-fall oral absorption-elimination curve, computing peak concentration (Cmax) and time to peak (Tmax) automatically.
Two-Compartment Model Alpha and Beta Phase Calculator - Calculates the alpha (distribution) and beta (elimination) hybrid rate constants, coefficients A and B, and biphasic plasma concentration from the three underlying micro-rate constants.
For weight-based dosing, blood pressure, and other clinical reference tools, see the Medical subcategory.
Frequently Asked Questions
What is pharmacokinetics?
Pharmacokinetics is the study of how a drug moves through the body over time, its absorption, distribution, metabolism, and excretion. These four processes together determine how much of a drug reaches its site of action and for how long, which is exactly what half-life, clearance, and volume of distribution describe mathematically.
What is the difference between half-life and elimination rate constant?
They describe the same first-order elimination process from two angles. Half-life is the time for concentration to fall by half, while the elimination rate constant (ke) is the fractional decline rate per unit time, related by t1/2 = ln(2)/ke. The Drug Half-Life Calculator and Elimination Rate Constant Calculator convert between the two.
Why is volume of distribution not a real physical volume?
Volume of distribution (Vd) is a proportionality constant that relates the dose given to the resulting plasma concentration, not an anatomical space. Drugs that bind heavily to tissue can have a calculated Vd far larger than a person's actual body volume. The Volume of Distribution Calculator explains this in more depth with a tissue-distribution classification.
What is the difference between a one-compartment and a two-compartment model?
A one-compartment model treats the whole body as a single well-mixed pool, producing a single-exponential decline. A two-compartment model separates blood from peripheral tissue, producing a biphasic curve with a fast early distribution phase (alpha) and a slower terminal elimination phase (beta). The Two-Compartment Model Alpha and Beta Phase Calculator computes both phases from the underlying micro-rate constants.
Can I use these calculators to determine a real medication dose?
No, never. These calculators illustrate standard pharmacokinetic formulas for educational purposes only. They have no drug database, do not know a specific medication's safe range or contraindications, and cannot account for kidney or liver function, drug interactions, or individual patient factors. Always follow the exact dose prescribed by a doctor or pharmacist.