Peptide & drug half-life calculator
How long does it actually stay in your system? Pick a peptide or drug — or enter your own half-life — and the time since your last dose, and see the percent remaining now, when it falls to 50, 25, 5 and 1%, and when it’s effectively cleared. A pharmacology estimate, not medical advice.
Semaglutide half-life ~7 days · FDA label
Remaining now
- Time from your last dose to…
Effectively cleared (~97%, five half-lives): 35 days
A single-compartment estimate (remaining = ½^(time ÷ half-life)). It doesn’t model repeat-dose buildup or depot esters, and it is not an anti-doping detection window — assay sensitivity means a drug is often detectable long after it’s functionally cleared.
Why half-life explains the dosing schedule
Half-life is simply the time for half of a dose to leave the body, and it decides almost everything about how a compound is dosed. A peptide with a 12-minute half-life like sermorelin is essentially gone within an hour, which is why it’s dosed at night to mimic a natural pulse; a molecule engineered to last days, like CJC-1295 with DAC or a weekly GLP-1, holds a steady level you don’t feel rise and fall. The same math explains why a testosterone ester is injected once or twice a week, not daily. The presets here are limited to reasonably well-characterized compounds with their source noted; many research peptides (BPC-157, TB-500) have poorly defined human half-lives, so we don’t pretend to a precise number. For the dosing side of the picture, see the reconstitution calculator and our peptide dosage guides.
Common questions
- How do you calculate how much of a drug is left after a given time?
- Each half-life cuts the amount in half, so the fraction remaining = ½ raised to (time elapsed ÷ half-life). After 1 half-life 50% is left, after 2 it's 25%, after 3 it's 12.5%, and after about 5 half-lives roughly 97% has cleared. Enter the compound and the time since your last dose and this tool does the arithmetic.
- How long does sermorelin / CJC-1295 / ipamorelin stay in your system?
- It varies enormously by molecule. Sermorelin has a very short half-life (~12 minutes), so it's gone within hours; ipamorelin is ~2 hours; but CJC-1295 with DAC is engineered to last ~6–8 days. That huge spread is exactly why dosing frequency differs between peptides, and the calculator shows it for each preset.
- Does this tell me a doping / drug-test detection window?
- No — and that's an important distinction. Clearance (how much active drug is left) is not the same as a detection window. Sensitive anti-doping and lab assays can detect a substance or its metabolites long after it's functionally cleared from a half-life standpoint. Treat this as a pharmacology estimate, not a testing-window guarantee.
- Why aren't BPC-157 or TB-500 in the presets?
- Because their human half-lives are poorly characterized — the published figures are inconsistent and mostly from animal or in-vitro work — so a precise preset would be false precision. You can still use the calculator by entering a custom half-life, but treat any single number for those research peptides with caution.
- Is this a single-dose or steady-state estimate?
- Single-dose. It models the decline of one dose and ignores accumulation from repeat dosing and depot-ester release. For long-half-life compounds taken regularly (e.g. testosterone esters or weekly GLP-1s), levels build up over several half-lives to a steady state that's higher than any single dose — a separate calculation.