Drug Half Life Calculator
Illustrate one-compartment decay from an exact product half-life while blocking dosing, safety and drug-test clearance claims. Sensitive inputs stay in your browser.
The displayed fraction is the one-compartment equation 0.5^(elapsed ÷ half-life). FDA labeling distinguishes effective and terminal half-life and may describe active metabolites, nonlinear elimination and population variability. Review note: Verify the exact product half-life.
Context matters.
- Do not use a half-life multiple to decide when to stop or repeat medicine, drive, breastfeed, undergo a procedure or assume an overdose is safe.
- The exact formulation, dose, repeated dosing, kidney or liver function, age, interactions, active metabolites and effective versus terminal half-life can materially change exposure.
- A predicted fraction cannot tell whether a drug test will be negative; test type, analyte, cutoff and specimen collection control the reported result.
Sources & scope
The calculation guide and this source trail show what the result means, where the rule came from and when it was last reviewed. This is source-and-calculation QA, not a claim of medical, legal, tax or other professional review; time-sensitive decisions still belong with the linked authority.
A visible path from input to answer.
Illustrate one-compartment decay from an exact product half-life while blocking dosing, safety and drug-test clearance claims. The page keeps the calculation scope and its limits beside the result so the output can be checked, copied or revisited.
- Read the record. The calculator uses Medication or substance, Half-life from the selected source (hours), Hours since the reference dose / time, Half-life source and Dosing context and 3 additional fields supplied in the form.
- Apply the scope. It applies the Pharmacokinetic education — exact FDA prescribing-information half-life; never a dosing, safety or test-clearance result reference and the explicit date, unit and counting conventions shown in the result.
- Expose the checkpoints. Intermediate rows, warnings and timeline events stay visible; the emphasized row identifies the primary checkpoint when one exists.
The displayed fraction is the one-compartment equation 0.5^(elapsed ÷ half-life). FDA labeling distinguishes effective and terminal half-life and may describe active metabolites, nonlinear elimination and population variability. Review note: Verify the exact product half-life.
- Half-life entered12 hours
- Mathematical parent-drug fraction6.25%
- Metabolite / kinetics checkNot checked
Calculation purpose: Illustrate one-compartment decay from an exact product half-life while blocking dosing, safety and drug-test clearance claims. This is a high-sensitivity reference output; the linked authority or qualified professional controls the final decision.
Numeric inputs are constrained by the field limits and the result keeps the entered units visible. Zero, minimum, maximum and non-finite values are treated as input boundaries.
Rule set 2.0.0 · Last reviewed 2026-08-20 · Next review due 2027-02-20. The source panel below contains the linked evidence.
What to know before using the result.
Does five half-lives mean a medicine is safe or completely gone?
No. The mathematical amount is about 3.1% after five identical half-lives, but active metabolites, repeated dosing, nonlinear kinetics and individual factors can change clinical effects and risk.
What is the difference between effective and terminal half-life?
The effective half-life better reflects accumulation during repeated dosing, while a terminal half-life may describe a slow final phase. The correct value must come from the exact product's authoritative information.
Can this calculator predict a drug-test result?
No. Drug testing depends on specimen, analyte, cutoff, collection timing and confirmation methods. The half-life math is not a clearance, dosing or pass-test prediction.