What a half-life actually means

It is the time for the amount in your body to fall by half. After one half-life you have 50% of a dose left, after two 25%, after three 12.5%. The practical rule that follows: a compound is substantially cleared after about four to five half-lives, and it takes roughly the same number of half-lives of regular dosing to build up to a stable level.

That is why a compound with a 5-hour half-life behaves completely differently on a daily schedule than one with a 7-day half-life, even at the same milligrams.

Steady state is why week three feels different

If you dose more often than the compound clears, it accumulates: each dose lands on top of what is left of the last. The level climbs and then flattens once elimination matches intake — steady state. For a weekly compound with a week-long half-life, that is roughly four to five weeks in, which is exactly when people report that things “settled”.

It also means an early side effect that fades is a different signal from one that appears in week four.

Why the peak is not always the same height

A peak is your new dose plus whatever has not cleared yet, so on an accumulating schedule each peak sits a little higher than the last until steady state. A chart that draws every peak at the same height is not modelling anything — it is drawing your dose amount.

This is subtle enough to get wrong: an earlier version of our own chart sampled the curve on a fixed grid rather than at the moment of each dose, which drew fast-clearing compounds anywhere between their real peak and a fraction of it. Peaks are now measured at the dose.

What this changes about tracking

• Timing matters as much as amount. Log when you actually dosed, not when you intended to.
• A missed dose is not a gap, it is a dip. How big depends entirely on the half-life.
• Splitting a dose changes the shape, not the total. Two half doses give a flatter curve.
• Stacking compounds needs one chart. Separate lists cannot show you overlap.

Where the numbers come from

Half-lives vary with route, formulation and the person, which is why the compound library gives a range rather than a single figure, and says where it comes from. BioHack Track models each logged dose against that half-life and draws what is still circulating — free, with no history limit. It is a model, not a blood test, and it is worth holding it as such.

Questions

Is a modelled level the same as a blood level?

No. It is a first-order decay model from a published half-life, not a measurement. It is useful for timing and for seeing accumulation and gaps; it is not a substitute for bloodwork.

How long until a compound is out of my system?

Roughly four to five half-lives leaves only a few percent. For a 5-hour half-life that is about a day; for a 7-day half-life it is a month or more.

Can it chart several compounds at once?

Yes — that is most of the point. Overlapping protocols are drawn on the same timeline so you can see where they coincide.

Is the levels chart free?

Yes. Dose logging and the levels chart are free on both iOS and Android, with no history limit.