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Drug Half Life Elimination Calculator

Work out drug half life elimination instantly with clear inputs, formula shown and shareable results.

About Drug Half Life Elimination Calculator

Applies first-order elimination to find the concentration remaining after a given time, together with the elimination rate constant.

Formula

First-order elimination

C(t) = C0 x 0.5^(t / half-life); elimination rate constant ke = ln 2 / half-life

Worked example

With the default values below, Drug Half Life Elimination Calculator returns Concentration remaining of 12.5000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Starting concentrationaccepts 0.01–10,000 mg/L
100 mg/L
Elimination half-lifeaccepts 0.1–500 h
6 h
Time elapsedaccepts 0–2,000 h
18 h

Results

Concentration remaining
12.5000 mg/L
Percentage remaining
12.500%
Half-lives elapsed
3.00
Elimination rate constant
0.1155 per h

Step by step

  1. 1Values used
  2. 2First-order elimination
  3. 3Concentration remaining= 12.5000 mg/L
  4. 4Percentage remaining= 12.500
  5. 5Half-lives elapsed= 3.00
  6. 6Elimination rate constant= 0.1155 per h

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

How many half-lives clear a drug?

About 97% is gone after five half-lives and over 99% after seven.

Does this apply to all drugs?

Only to first-order kinetics. Phenytoin, alcohol and high-dose salicylate show saturable zero-order elimination.

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