Medication Half-Life and Clearance Calculator
Calculate drug concentration over time using half-life.
Find time to steady state, time to clearance (5 half-lives), and peak/trough concentrations for pharmacokinetics.
MEDICAL DISCLAIMER This calculator is for pharmacology education only. Never use this to adjust medication doses or timing without consulting your prescribing physician or pharmacist.
Drug Half-Life The biological half-life (t½) is the time required for the drug concentration in the body to fall by 50%. After 1 half-life: 50% of drug remains. After 2 half-lives: 25% remains. After 5 half-lives: ~3.1% remains — considered clinically cleared. Formula: C(t) = C₀ × (0.5)^(t/t½) = C₀ × e^(−0.693t/t½)
Common Drug Half-Lives Very short (< 1 hour): adenosine (6 sec), epinephrine (< 5 min), insulin (5–10 min) Short (2–6 hours): ibuprofen (2h), acetaminophen (2–3h), aspirin (3–6h) Medium (6–24 hours): sertraline (26h), atorvastatin (14h), lisinopril (12h) Long (1–4 days): fluoxetine (1–4 days), amiodarone (40–55 days) Very long: chloroquine (1–2 months), digoxin (36–48h)
Steady State With regular dosing, drug levels reach steady state after ~4–5 half-lives. Steady-state concentration = (Dose × Bioavailability) / (Clearance × Dosing interval) Peak: right after dose. Trough: just before next dose. Steady state has a therapeutic window — too low: no effect; too high: toxicity.
Loading Dose To achieve steady-state concentrations immediately, a loading dose is sometimes given. Loading dose = Target concentration × Volume of distribution Common for drugs with long half-lives (digoxin, amiodarone, phenytoin).
Elimination Rate Constant k_el = 0.693 / t½ C(t) = C₀ × e^(−k_el × t) Volume of distribution (Vd) relates blood concentration to total body drug: Dose = Vd × C