Half-life calculator
One-compartment oral absorption model — plot concentration vs time.
Peak (Cmax)
—
mg/L
Time to peak (Tmax)
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h
At 8 h
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mg/L
5 half-lives
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h (elimination)
Concentration at key time points
| Time (h) | Conc (mg/L) | % of Cmax |
|---|
Frequently asked questions
How many half-lives until a drug is fully eliminated?
After 4–5 half-lives, ~94–97% of the drug has been eliminated. Clinically, "full elimination" is set at 5 half-lives. Steady state during repeat dosing is also reached in ~4–5 half-lives. See NCBI StatPearls on pharmacokinetics and the DrugTheGuide half-life glossary entry for an interactive simulator.
Where do I find the half-life of a specific drug?
The half-life is in the Clinical Pharmacology → Pharmacokinetics section of the FDA-approved label. Search for any approved drug on DailyMed. For ibuprofen specifically, the label lists t½ ≈ 2 h. The PubChem compound page also aggregates PK data.
Is this a one-compartment model?
Yes, this uses a one-compartment first-order elimination model: C(t) = C₀ · e−0.693t/t½. It fits most small-molecule drugs with single-phase decay. For bi-exponential drugs (digoxin, vancomycin), a two-compartment model is more accurate. The FDA non-compartmental analysis guidance describes how PK parameters are estimated from study data.
What is the difference between half-life and dosing interval?
Half-life is a PK property; dosing interval is a clinical decision. A common rule: dose every 1–2 half-lives to keep troughs above MEC. Drugs with t½ > 24 h can often be dosed once daily or less (e.g., amlodipine t½ 35–50 h). See the full discussion in the NCBI PK chapter and ASHP clinical references.