The Peptide Calculator

Half-life curve

Enter a published half-life to see the shape of the arithmetic. The curve describes a model, not a person.

Educational arithmetic only. Not medical advice and not a dosing protocol.

From a named source. This site holds no half-life table.

Fill in the fields above to see the answer.

Read this with the answer

This is educational arithmetic on figures entered by the reader. It is not medical advice, not a dosing protocol, and not a recommendation that anything be prepared, obtained or administered.

Nothing here states what quantity is appropriate for anyone, and there is no function in it that produces an amount to administer. A question about anyone’s health belongs with a licensed clinician who can examine the person asking.

Most compounds named here are research chemicals that are not approved by the FDA for human use. An exact calculation is not an accurate measurement: what is actually in a syringe depends on the preparation and the device, neither of which this page can see.

A half-life belongs to the population, formulation and route it was measured in. Transferring one to any other context is an assumption, not a calculation, and this page performs no such transfer: it plots the figure entered.

No qualified clinical reviewer is recorded against this site, and no credential is claimed anywhere on it. Full disclaimer.

Show the working
  1. The fraction remaining is 0.5t / t½. At whole multiples of the half-life that is exactly 1 / 2n: 50%, 25%, 12.5%, 6.25%, 3.125%.
  2. Between those points the exponent is fractional and the value is irrational, so unlike the rest of this site the curve is computed in floating point and is labelled approximate everywhere it is shown.
  3. The curve is a single-compartment model: it assumes the full amount is immediately available and leaves at a constant proportional rate. Neither assumption holds for a subcutaneous injection, where absorption takes time and competes with elimination.

What this curve leaves out

Absorption, distribution between tissues, protein binding, active metabolites, and the variation between one person and another are all absent from it. A real concentration-time curve after a subcutaneous injection rises before it falls, because the compound has to get in before it can be cleared, and this model has no rising limb at all.

What the curve is good for is the shape of the arithmetic: how quickly a given half-life brings an amount down, why five half-lives is the usual rule of thumb for "most of it has gone", and why doubling a half-life does not double the time to clear.

Why no half-life is supplied

A half-life is a measurement, and it belongs to the study that measured it: the species, the formulation, the route, the dose range and the assay all travel with the number. The same compound can have several published half-lives that differ by more than the precision anyone would quote them to.

So this page asks for one rather than holding a table. Published values and the records they came from are on the research corpus this site links out to, where each figure sits next to its citation and the population it was measured in.

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