Peptide Half-Life Calculator

Understanding Peptide Half-Life

Every peptide has a half-life — the time it takes for half of the active drug to leave your bloodstream. A 4-hour half-life means if you injected 250mcg at 8am, about 125mcg would remain at noon, 62mcg at 4pm, and so on. This decay follows first-order kinetics, which means the relative fraction cleared per unit of time is constant.

Why It Matters

Half-life dictates how often to dose. For a peptide with a 4-hour half-life (like BPC-157), once-daily dosing produces wild swings between peaks and troughs. Splitting into 2–3 smaller doses keeps blood levels more stable. For a peptide with a 168-hour half-life (like semaglutide), weekly dosing is sufficient because blood levels only halve between doses.

Steady State

When you dose repeatedly at a fixed interval, blood levels climb and eventually plateau — the amount incoming per dose equals the amount cleared over the interval. This is called steady state. It takes roughly 5 half-lives to reach 97% of steady state. For a 4-hour half-life peptide that's ~20 hours; for a 168-hour half-life it's 35 days.

The Math

C(t) = C₀ · e^-k·t, where k = ln(2) / half-life

When multiple doses overlap, we just sum: C(t) = Σ dose_i · e^{-k·(t - t_i)} for every prior dose at time t_i. That's the curve you see above.

Common Questions

Related Tools