Tool
Generic half-life calculator
Use this generic tool with any half-life value. For substance-specific presets and references, open the dedicated substance pages.
Calculator
Every curve begins at 100%. No dose or measured body concentration is assumed.
X-axis: elapsed time. Y-axis: modeled percentage of the relative starting point remaining. This is a mathematical visualization, not a personal concentration estimate.
What this calculator shows
The calculator visualizes a normalized first-order half-life curve. Enter a half-life in hours and an elapsed time. The chart then estimates the percentage of the relative starting point that remains under the simplified equation C(t) = C0 x (1/2)^(t / t1/2).
This is useful for seeing the shape of exponential decline: the curve drops quickly at first, then flattens as the remaining amount gets smaller. One half-life leaves 50%, two half-lives leave 25%, three leave 12.5%, and five leave about 3.1% in this simplified model.
How to choose a half-life value
Use a half-life value from a reliable source and check what it represents. Some sources report a terminal half-life, some report an effective half-life, and some report values for specific formulations, routes, or study populations.
If a substance has active metabolites or multi-phase kinetics, one half-life number will not describe the full concentration-time profile. For that reason, HalfLifeDB treats this page as a concept tool, not a personalized concentration or clearance estimate.
What the result does not mean
- It does not estimate impairment, safety, intoxication, or ability to drive.
- It does not predict urine, blood, saliva, breath, or hair testing results.
- It does not account for repeated dosing, tolerance, withdrawal, interactions, or organ function.
- It does not provide dosing, redosing, treatment, or medication-change advice.