Half-life calculator

Half-life questions

How is the amount remaining calculated?

Remaining = dose × 0.5^(time elapsed ÷ half-life). Divide the elapsed time by the half-life to get the number of half-lives that have passed, raise one half to that power for the fraction left, and multiply by the dose for the amount. Show work prints all three steps.

How long until a dose is effectively cleared?

About 6.6 half-lives to fall to 1%, and about 4.3 to fall to 5%. The clearance timeline lists those milestones in hours, days or weeks for the half-life you picked, and marks the ones the time you entered has passed.

Do I need to enter my dose?

Not for the percentage. The fraction remaining depends only on the half-life and the time, so it shows straight away. The amount remaining is that fraction of your dose, so it appears once you enter one. The calculator never fills in a dose for you. For compounds a published trial or a drug label gives a fixed dose, those doses are listed with links to their sources, and one tap enters one.

Where do the half-lives come from?

Each compound in the list carries a typical published or commonly cited half-life. They are population averages, sources vary, and individual variation is large. If you have a better figure, choose Custom half-life and type it in.

Is this the same as my blood level?

No. It models one dose as fully present at the moment of injection and cleared at a constant rate. Depot injections such as oils release over hours to days, so early on the real level lags the curve. Treat it as a model of the arithmetic, not a measurement.

Does this give medical advice?

No. It performs arithmetic on numbers you enter. It does not tell you when or whether to take a dose. For medical decisions, consult a qualified healthcare professional.