Quick answer: In the model, Tirzepatide drops below 3.1% of its peak about day 26 after your last dose (about 3.5 weeks). The arithmetic is 5 half-lives of about 5 days = 25 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 6.
How long does Tirzepatide stay in your system?
Tirzepatide has a half-life of about 5 days: every 5 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. 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 6, three quarters by about day 11, and after 5 half-lives (25 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 25 days
The 25-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 26.
What this tool does not tell you
This calculator computes no waiting period of its own. Here is what each label says about surgery and pregnancy, quoted from the prescribing information. None gives a taper schedule.
Mounjaro label
- Surgery: no waiting period. Section 5.9 says to "inform healthcare providers prior to any planned surgeries or procedures".
- Pregnancy: no waiting period before a planned pregnancy.
Source: Mounjaro Prescribing Information, DailyMed setid d2d7da5d-ad07-4228-955f-cf7e355c8cc0, effective 2026-08-27.
Zepbound label
- Surgery: no waiting period. Section 5.9 says to "inform healthcare providers prior to any planned surgeries or procedures".
- Pregnancy: no waiting period before a planned pregnancy; section 8.1 says: "Advise pregnant patients that weight loss is not recommended during pregnancy and to discontinue ZEPBOUND when a pregnancy is recognized".
Source: Zepbound Prescribing Information, DailyMed setid 487cd7e7-434c-4925-99fa-aa80b1cc776b, effective 2026-08-28.
The calculator shows modelled drug levels only: not when effects or side effects wear off, and not how long a drug test could detect it.
Frequently asked questions
How long does Tirzepatide stay in your system?
In the model, the amount of Tirzepatide in your body peaks about 1 day after your last weekly dose, falls to half of that peak by about day 6, and drops below 3.1% of the peak by about day 26. The arithmetic: a half-life of about 5 days means 5 half-lives is 5 x 5 = 25 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 Tirzepatide is left after 2 weeks?
In the model, about 44% of the peak is left one week after your last dose, 17% after two weeks, 2% after four weeks and 0.3% 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 Tirzepatide stay in your system after one dose?
Set the weeks to 1. In the model a single dose peaks about 1 day after the injection and drops below 3.1% of that peak by about day 26. After 12 weekly doses the model gives about day 26: 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. For surgery, the Mounjaro and Zepbound labels give no waiting period; they say to "inform healthcare providers prior to any planned surgeries or procedures". For pregnancy, the Mounjaro and Zepbound labels give no waiting period before a planned pregnancy; the Zepbound label (section 8.1) says: "Advise pregnant patients that weight loss is not recommended during pregnancy and to discontinue ZEPBOUND when a pregnancy is recognized". This tool shows modelled drug levels only, not how long a drug test could detect it.
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 Tirzepatide: half-life about 5 days, time to peak 1 day (Zepbound label: median 24 hours, range 8 to 72 hours), and 80% bioavailability. 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: Tirzepatide is the active ingredient in FDA-approved GLP-1 medications. 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.