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Peptide half-life & active-level calculator
See how a compound accumulates to steady state at your dose and schedule — the estimated active amount over time, plus peak and trough once it levels off.
Your schedule
Example numbersEstimated level over 28 days
- Week 4 peak
- 3.84 mg
- Week 4 trough
- 1.93 mg
- To steady state
- ~5 wk
Estimate from a published/typical half-life (one-compartment model), not a measurement. Real levels vary with absorption, body weight, and the specific compound. Use it to understand the shape of accumulation, not as a target.
What half-life means for your protocol
A compound's half-life is how long it takes for half of it to clear. Each dose stacks on what's left of the previous ones, so levels climb until what you take each interval equals what you clear — that plateau is steady state, reached after roughly five half-lives.
This is why a long-half-life GLP-1 like semaglutide or retatrutide feels different at week 4 than week 1 — it's still building. Short-half-life peptides clear between doses, so their curve spikes and falls rather than plateauing high.
Example: semaglutide, with a half-life of about 7 days, taken at 2 mg once weekly reaches steady state in about 5 weeks. In week 4 its estimated peak is 3.84 mg and its trough 1.93 mg.
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