Half-Life Calculator
Calculate drug elimination half-life using multiple methods
Elimination Kinetics
Calculation Method
Units
Elimination Rate Constant (kₑ)
Formula
t½ = 0.693 ÷ kₑ
Example Drugs
Half-Life Results
Elimination Half-Life (t½)
Enter Values
Elimination Pattern
1 × t½
50%
2 × t½
25%
3 × t½
13%
4 × t½
6%
5 × t½
3%
Quick Reference
Steady State~4-5 × t½
Loading DoseBased on Vd
Dosing Interval~1 × t½
Pharmacokinetic Relationships
Elimination Rate Constant (kₑ)
• kₑ = 0.693 ÷ t½
• kₑ = Cl ÷ Vd
• Units: time⁻¹ (h⁻¹)
• Represents fraction eliminated per unit time
Clearance (Cl)
• Volume of plasma cleared per unit time
• Cl = kₑ × Vd
• Units: volume/time (L/h)
• Independent of concentration for first-order kinetics
Volume of Distribution (Vd)
• Apparent distribution volume
• Vd = Dose ÷ C₀
• Vd = Cl ÷ kₑ
• Theoretical, not physiological volume