Clearance estimator.
Exponential decay on the numbers you enter. Pick one of the 24 compounds with a published human half-life to pre-fill the field, or type any value, and see what the simplest pharmacokinetic model says remains after a given time. It is a model, not a measurement.
Show the math
How it works.
Pick a compound, or type a half-life
Choosing a compound pre-fills the published human half-life from our sourced half-life reference, and the field stays editable. If the compound you care about has no published value, or you want to see how sensitive the answer is to the input, type your own number instead.
Enter a starting amount and a time elapsed
The starting amount can be in any unit you like, because the model is purely proportional. Whatever you put in is the unit that comes out. Time elapsed switches between hours and days so that compounds with half-lives measured in minutes and in weeks both stay readable.
Read the curve, not the number
You get the amount remaining, the percentage remaining and cleared, how many half-lives have elapsed, and the modelled time to 95% and 99% cleared. The last two are where the intuition lives: clearance is exponential, so the tail is much longer than most people expect.
What this model leaves out.
One compartment, first order, single dose. That is the whole model, and every simplification in it is a place where reality diverges. Real plasma curves are at least two-compartment: a fast distribution phase as the compound spreads into tissue, then a slower elimination phase. Early on, the real concentration falls faster than this curve predicts. Later, it can fall more slowly.
Route matters too. For a subcutaneous depot the observed decline often reflects how fast the compound leaves the injection site rather than how fast the body destroys it, which is called flip-flop kinetics. Several values in the picker are explicitly labelled apparent for this reason, including somatropin and afamelanotide. And individual variation is large: renal and hepatic function, body composition, protein binding and formulation all move the number, which is why published figures come with standard deviations that are sometimes as large as the value itself.
Finally, this models one dose from one point in time. Repeated administration accumulates toward a steady state, typically reached after about four to five half-lives, and none of that is represented here. Use it to understand the shape of exponential decay. Do not use it as a washout guarantee, a drug-test prediction, or a reason to take or skip anything.
Every value in the picker is taken from an FDA label or a peer-reviewed pharmacokinetic study, with its source linked next to it the moment you select a compound. Nothing is averaged, extrapolated from animals, or borrowed from a vendor page. The half-life reference lists all of them with full citations, and also lists the compounds where a number circulates online with no reliable human data behind it.
FAQ.
What model is this and how accurate is it?
It is one-compartment first-order decay, remaining equals start multiplied by 0.5 raised to the power of time divided by half-life. That is the simplest curve in pharmacokinetics and it is an approximation of a real plasma profile, not a reproduction of one. Real curves have a distribution phase before the elimination phase, and for subcutaneous administration the shape is often governed by absorption rather than elimination. Treat the output as the rough shape of a curve.
Why does 95% cleared take more than four half-lives?
Because decay is exponential, not linear. Each half-life removes half of whatever is left, so you approach zero without ever arriving. After four half-lives about 93.75% is gone, and 95% takes about 4.32 half-lives. Ninety-nine percent takes about 6.64. The formula is half-life multiplied by the natural log of 20 or 100, divided by the natural log of 2.
Can I use this to work out when to take something?
No. Dosing intervals come from clinical trials that measured outcomes and tolerability, not from arithmetic on a half-life, and this site does not suggest, default to, or recommend any amount or schedule anywhere. This tool exists to build intuition about exponential decay. It is not a dosing tool and it will not become one.
Will this tell me if something will show up on a drug test?
No, and it would be a mistake to use it that way. Detection depends on the assay, its limit of detection, the matrix being sampled, metabolites rather than parent compound, and individual variation. A plasma decay model says nothing about any of those. If a testing outcome matters to you, ask the testing authority, not a calculator.
Does this model repeated doses or accumulation?
No. It models a single starting amount decaying from one point in time. Repeated administration accumulates toward a steady state, and that behaviour is not represented here at all. Using the single-dose output to reason about an ongoing pattern will understate what is present.
Why do so few compounds appear in the picker?
Because the picker only offers compounds where a published human half-life exists and we could trace it to a primary source. Most research peptides have no such value. The half-life reference explains which compounds those are and what the evidence actually consists of, and the manual entry field is there for every other case.