Drug Half-Life Elimination Calculator
Drug Elimination Timeline
Calculate how much of a drug remains after a given time based on its half-life.
mg
Common Drug Half-Lives
Look up the half-life of common medications and calculate elimination time.
mg
hours
Formula
Amount Remaining = Initial_Dose × (1/2)^(Time / Half_Life). Percent Remaining = (Remaining / Initial) × 100. Time to ~97% elimination = 5 × Half_Life.
Frequently Asked Questions
What is a drug's half-life?
A drug's half-life is the time it takes for the concentration of the drug in the body to decrease by half. After one half-life, 50% remains; after two half-lives, 25% remains; after five half-lives, less than 3.2% remains, which is considered effectively eliminated.
How many half-lives until a drug is out of your system?
It takes approximately 5 half-lives for a drug to be considered effectively eliminated from the body (96.875% cleared). For practical purposes, 5-7 half-lives is the standard pharmacological washout period.
Does half-life affect how often I take medication?
Yes. Drugs with short half-lives (e.g., ibuprofen at 2-4 hours) need to be taken more frequently, while drugs with long half-lives (e.g., fluoxetine at 1-3 days) can be taken once daily. Dosing intervals are typically designed to maintain therapeutic drug levels.