Retatrutide Half-Life Calculator
Retatrutide's reported half-life supports weekly administration, which is why its pharmacokinetics get discussed as though it were an established weekly medication. It is not — it is investigational, unapproved, and this calculator models the shape of the curve rather than endorsing anything about running it.
Half-life 6 days · peaks at 40 hours
Every 7 days.
Half-life
Left at next dose
Retatrutide · once weekly · levels plateau after ~30 days
Steady-state peak
1.79 mg
Steady-state trough
0.96 mg
Accumulation
1.8×
At once weekly, each dose lands before the previous one has cleared, so levels stack to about 1.8× a single dose before plateauing — roughly 30 days in. After the last dose it takes about 30 days to clear.
This is a modelled estimate of relative levels from published half-life and time-to-peak figures — not a measured blood concentration. Individual pharmacokinetics vary.
Based on a published Retatrutide half-life of about 6 days. The chart models RELATIVE levels from a unit dose — enter your own figures to see the shape. It is not a dose recommendation.
Never do this math twice.
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What a 6 days half-life means in practice
A half-life of 6 days against once a week dosing means each dose lands before the previous one has gone. That changes the curve in three ways:
1. One half-life
Half the dose is gone after 6 days. After two half-lives 25% remains, after three 12.5%.
2. What's left at the next dose
Dosing once a week means the next dose lands 7 days later, with about 45% of the previous one still present.
3. Accumulation and plateau
Those leftovers stack until intake matches elimination — about 1.8× a single dose, reached after roughly 30 days (five half-lives).
Worked example
Retatrutide has a half-life of 6 days. Dosing once a week, the next dose arrives 7 days later with about 45% of the previous one still on board. Levels therefore stack to roughly 1.8× a single dose before plateauing, which takes about 30 days — and after a final dose it takes about the same again to clear.
A six-day half-life inside a seven-day interval
Retatrutide's reported half-life sits just under a week, which places it between tirzepatide and semaglutide on the accumulation spectrum. Enough of each dose survives the interval to stack, so levels climb across the first several weeks before plateauing rather than repeating the same curve from the start.
The practical consequence of any half-life close to the dosing interval is that early weeks and later weeks are not comparable. Anything observed in week two is happening at a materially lower average level than the same routine produces in week six, which is why comparing early experience against later experience is misleading unless the plateau is accounted for.
The regulatory position matters more than the arithmetic here. Retatrutide has no approval in any jurisdiction and no licensed supply — the background on what retatrutide is covers what that actually means, including why no compounding pathway exists for it.
Frequently asked questions
This calculator is provided for informational and educational purposes only and is not medical advice. Always confirm dosing with a qualified healthcare professional and double-check your own measurements before administering anything.
Built by the Pep AI team.