Quick answer: In the model, Semaglutide drops below 3.1% of its peak about day 37 after your last dose (about 5.5 weeks). The arithmetic is 5 half-lives of about 7 days = 35 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 9.
How long does Semaglutide stay in your system?
Semaglutide has a half-life of about 7 days: every 7 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 1.5 days while that dose is absorbed (sooner than the 2 days after a single dose, because the earlier doses are already falling). 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 9, three quarters by about day 16, and after 5 half-lives (35 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 35 days
The 35-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 37.
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.
Ozempic label
- Surgery: no waiting period. Section 5.10 says to "inform healthcare providers prior to any planned surgeries or procedures".
- Pregnancy: section 8.3 says: "Discontinue OZEMPIC in women at least 2 months before a planned pregnancy due to the long washout period for semaglutide."
Source: Ozempic Prescribing Information, DailyMed setid adec4fd2-6858-4c99-91d4-531f5f2a2d79, effective 2026-06-01.
Wegovy label
- Surgery: no waiting period. Section 5.10 says to "inform healthcare providers prior to any planned surgeries or procedures".
- Pregnancy: section 8.3 says: "Because of the potential for fetal harm, discontinue WEGOVY in patients at least 2 months before they plan to become pregnant to account for the long half-life of semaglutide."
Source: Wegovy Prescribing Information, DailyMed setid ee06186f-2aa3-4990-a760-757579d8f77b, effective 2026-06-18.
The 2-month interval before a planned pregnancy is longer than this tool's 3.1% line (about day 37), so the modelled date is not a pregnancy-planning date.
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 Semaglutide stay in your system?
In the model, the amount of Semaglutide in your body peaks about 1.5 days after your last weekly dose, falls to half of that peak by about day 9, and drops below 3.1% of the peak by about day 37. The arithmetic: a half-life of about 7 days means 5 half-lives is 5 x 7 = 35 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 Semaglutide is left after 2 weeks?
In the model, about 62% of the peak is left one week after your last dose, 31% after two weeks, 8% after four weeks and 2% 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 Semaglutide stay in your system after one dose?
Set the weeks to 1. In the model a single dose peaks about 2 days after the injection and drops below 3.1% of that peak by about day 38. After 12 weekly doses the model gives about day 37: 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 Ozempic and Wegovy labels give no waiting period; they say to "inform healthcare providers prior to any planned surgeries or procedures". For pregnancy, the Ozempic label (section 8.3) says: "Discontinue OZEMPIC in women at least 2 months before a planned pregnancy due to the long washout period for semaglutide." The Wegovy label (section 8.3) says: "Because of the potential for fetal harm, discontinue WEGOVY in patients at least 2 months before they plan to become pregnant to account for the long half-life of semaglutide." That is longer than this tool's 3.1% line (about day 37), so the modelled date is not a pregnancy-planning date. 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 Semaglutide: half-life about 7 days, time to peak 2 days (Wegovy label: 1 to 3 days after a dose; the model uses the midpoint), and 89% 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: Semaglutide 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.