WeightSnap Tools / Half-life calculator
How long does semaglutide, tirzepatide, or retatrutide stay in your system? Pick a medication and see the decay curve, a table by half-life, and the time to near-complete clearance. You can edit the half-life for any drug or a custom peptide.
| Half-lives elapsed | Time | Remaining |
|---|
Every half-life, the amount remaining halves: 100% becomes 50%, then 25%, then 12.5%, and so on. Medications are generally considered effectively cleared after about five half-lives, when roughly 3% remains. The formula is a standard exponential decay:
Remaining fraction = 0.5 (time ÷ half-life)
So the only input that matters is the half-life. Longer half-life, longer it lingers. That is also why once-weekly GLP-1 medications take weeks, not days, to leave the body after a final dose.
| Medication | Elimination half-life | ~5 half-lives |
|---|---|---|
| Semaglutide (Ozempic, Wegovy, Rybelsus) | ~7 days | ~35 days |
| Tirzepatide (Mounjaro, Zepbound) | ~5 days | ~25 days |
| Retatrutide (investigational) | ~6 days | ~30 days |
| Dulaglutide (Trulicity) | ~5 days | ~25 days |
| Liraglutide (Saxenda, Victoza) | ~13 hours | ~3 days |
Values are approximate, from FDA prescribing information and published clinical literature. Retatrutide figures are from Eli Lilly's phase 2 data and may be refined; it is not yet FDA approved.
About 7 days per half-life, so roughly 35 days (five weeks) to near-complete clearance after the last dose. That is an average; individual clearance varies.
About 5 days per half-life, so roughly 25 days for near-complete clearance. It clears a little faster than semaglutide.
A reported half-life of about 6 days, so roughly 30 days to near-complete clearance. Retatrutide is investigational and not yet FDA approved.
Not exactly. Half-life is about blood concentration; felt effects like reduced appetite are related but vary person to person. This tool estimates clearance, not the timing of effects.
No. It applies a standard decay model to published half-life values for understanding only. Decisions about your medication belong with your prescriber.
WeightSnap is a tracking tool, not medical advice. This calculator applies a standard pharmacokinetic model to published average half-life values and makes no recommendations. Always work with your healthcare provider.
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