Quick answer: In the model, Retatrutide drops below 3.1% of its peak about day 32 after your last dose (about 4.5 weeks). The arithmetic is 5 half-lives of about 6 days = 30 days; the model lands a little later because the last dose is still being absorbed after you inject it. Half the peak is left at day 8.
How long does reta stay in your system?
Retatrutide has a half-life of about 6 days: every 6 days, the amount left in your body roughly halves. It never drops off a cliff. In the model, after your last weekly dose the level first rises for about 1 day while that dose is absorbed (sooner than the 1.5 days after a single dose, because the earlier doses are already falling); for Retatrutide the time to peak is the calculator's own assumption. After that it falls along the same half-life curve whether you took one dose or a year of them.
That is why the answer is a curve, not a single date. Half the peak is gone by about day 8, three quarters by about day 14, and after 5 half-lives (30 days of pure decay) about 3.1% is left. The calculator turns those days into dates from your own last injection and shows how much is left today.
Why the model lands after 30 days
The 30-day figure assumes the whole dose is in your body the moment you inject it. Under the skin, it is absorbed over a day or two, so the peak comes after the injection and every milestone shifts a little later: the model puts the 3.1% line at about day 32. For Retatrutide the time to peak is the calculator's own assumption, so that shift is approximate. The half-life sets almost all of the answer.
What this tool does not tell you
Retatrutide is investigational and has no FDA-approved label, so there is no label instruction on stopping, surgery or pregnancy to quote here. This calculator does not invent one. It shows modelled drug levels only: not when effects or side effects wear off, not how long a drug test could detect it, and not how long to wait before a procedure or a pregnancy. Ask the clinician who manages that decision.
Frequently asked questions
How long does reta stay in your system?
In the model, the amount of Retatrutide in your body peaks about 1 day after your last weekly dose, falls to half of that peak by about day 8, and drops below 3.1% of the peak by about day 32. The arithmetic: a half-life of about 6 days means 5 half-lives is 5 x 6 = 30 days, and 0.5^5 leaves 3.1% (about 97% gone). The model lands a little later because the last dose is still being absorbed after you inject it. Some drug remains after that, since the curve never reaches zero. Enter the date of your last dose above to see these as dates.
How much reta is left after 2 weeks?
In the model, about 54% of the peak is left one week after your last dose, 24% after two weeks, 5% after four weeks and 1.0% after six weeks. Some drug remains, since the curve never reaches zero. The percentages are the same at any dose; your dose only sets how many mg that is.
How long does reta stay in your system after one dose?
Set the weeks to 1. In the model a single dose peaks about 1.5 days after the injection and drops below 3.1% of that peak by about day 32. After 12 weekly doses the model gives about day 32: how long you took it changes how many mg build up, not how fast they leave.
Can I use this for surgery, pregnancy or a drug test?
No. Retatrutide is investigational and has no FDA-approved label, so there is no label instruction to quote, and this tool does not set a waiting period before surgery or pregnancy. It shows modelled drug levels only, not how long a drug test could detect it. Ask the clinician managing the surgery or pregnancy.
How is this calculated?
A one-compartment model with first-order absorption, the same model as the GLP3 Planner half-life calculator, for the injection. For Retatrutide: half-life about 6 days, time to peak 1.5 days, and 80% bioavailability. Retatrutide has no FDA-approved label: the time to peak is the calculator's own assumption and the bioavailability is inferred from tirzepatide, so treat its figures as approximate. Every weekly dose's curve is added together up to your last dose, and the tool reports what is left after it as a share of the peak that follows. The days and percentages do not depend on your dose or the bioavailability; those only set the mg.
The model parameters this page uses are the ones listed in the "How is this calculated?" answer above. Values marked as an assumption or as inferred could not be checked against a primary source.
Safety: Retatrutide is an investigational compound and is not approved by the FDA. This tool is educational only. It models population-average drug levels, not your own, and it does not tell you when to stop, restart or switch a medication. Talk to your prescriber before making any of those changes.