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GLP-1 Half-Life Calculator

The GLP-1 compounds sit within a few days of each other in half-life, and that small difference is what decides how much each accumulates on a weekly schedule. Each figure here carries the citation it came from — which is also why cagrilintide, the amylin analog this page once included, is no longer on it: the paper its half-life was attributed to turned out to be a QT study that states no half-life at all.

Last reviewed: September 21, 2026

A half-life and a schedule give a curve. Each dose decays on its own and the amounts add, which is what makes a compound accumulate or not.

Only compounds whose half-life Prof. Peptide can cite appear here. Half-life ~1 week. Source: FDA prescribing information (Wegovy / Ozempic).

Side by side at a once-weekly interval

Each compound’s own sourced half-life, modelled at a 168-hour (once-weekly) interval and a dose of 1 unit — the shared FDA-approved interval for all three, reported here to show what each half-life does at it, not as a recommendation:

CompoundHalf-lifeHalf-lives/intervalAccumulation ratio
Semaglutide168 h (~1 week)1.000×2.000
Retatrutide144 h (~6 days)1.167×1.803
Tirzepatide120 h (~5 days)1.400×1.610

All three are within a factor of two of each other in accumulation ratio at the identical interval — the differences are real but modest, since all three half-lives sit within a few days of the 168-hour week. Select any of the three in the calculator above to see its own chart.

This is a single-compartment model. It assumes each dose is fully present the moment it’s given and decays at a constant rate. It ignores absorption, distribution into tissue, and every difference between one person and another. It is the arithmetic of a half-life and a schedule, not a prediction about a body.

FAQ

glp1 half life comparison semaglutide tirzepatide retatrutide
At once-weekly dosing, the three differ in how much they accumulate because their half-lives sit at different points relative to the 168-hour interval: semaglutide (168 h) accumulates most, retatrutide (144 h) next, tirzepatide (120 h) least. All three are modelled as single-compartment arithmetic on the calculator above, each with its own FDA-label citation.
Which GLP-1 compound accumulates the most?
Of the three modelled here, semaglutide has the half-life closest to the once-weekly interval (168 hours against a 168-hour week) and the highest accumulation ratio of the three — about ×2.0 at steady state, for the same weekly dose repeated.
Why do semaglutide and tirzepatide accumulate differently if both are weekly?
Because their half-lives differ — semaglutide's FDA label states approximately one week (168 hours), tirzepatide's states approximately 5 days (120 hours). At the same once-weekly interval, tirzepatide's shorter half-life means more of each dose clears before the next one lands, producing a lower accumulation ratio (×1.61 against semaglutide's ×2.0).

For a single compound’s own dedicated page, see the semaglutide or tirzepatide half-life calculator.