GLP-1 Half-Life Calculator

Tirzepatide has an elimination half-life of about 5 days, so a Zepbound or Mounjaro dose falls below 5% of its steady level roughly 3 weeks after the last weekly injection. In practical terms, the medication is still doing most of its work a full week after an injection, which is exactly what a weekly schedule relies on: each new dose lands on about half of the previous one.

The label reports peak blood concentration a median of 24 hours after injecting (the range runs 8 to 72 hours), so levels actually rise for the first day or so before the long decline begins. Zepbound and Mounjaro are the same molecule, so everything on this page applies to both brands.

Semaglutide has an elimination half-life of approximately 1 week, the longest of the GLP-1 medications. The Wegovy label states that semaglutide remains in circulation for about 5 to 7 weeks after the last 2.4 mg injectable dose; this calculator's 5%-of-steady-level line falls at about 5 weeks, inside that same window.

The one-week half-life belongs to the molecule, not the package: Wegovy 2.4 mg, the higher 7.2 mg Wegovy HD dose, the Wegovy 25 mg daily tablet, Ozempic, and the Rybelsus tablets are all semaglutide, and all clear on the same weeks-long timeline. The tablets are taken daily because of how the oral form is absorbed, not because they leave the body faster: the Rybelsus label states semaglutide is present in circulation for about five weeks after the last tablet dose, and this calculator's curve agrees.

Liraglutide has the shortest half-life of the GLP-1 injections: 13 hours, with peak levels around 11 hours after the daily injection. A stopped course of Saxenda or Victoza is below 5% of its steady level in about 3 days, and regular dosing reaches steady state just as fast, in about 3 days.

That short half-life is why liraglutide is the one injectable dosed daily, and why its labels handle a missed dose by simply resuming the next day rather than making up the dose. Saxenda and Victoza are the same molecule at different doses; liraglutide has also been available as a generic since 2025.

Dulaglutide's elimination half-life is approximately 5 days, essentially the same as tirzepatide's, so Trulicity follows the familiar weekly-injection arithmetic: below 5% of its steady level about 3 weeks after the last injection, and close to steady state after about 4 weeks of weekly dosing. Peak levels arrive 24 to 72 hours after injecting, median 48.

Foundayo is the outlier: orforglipron has a half-life of approximately 29 to 49 hours after an oral dose, with peak levels 4 to 8 hours after taking the pill. At that pace it is essentially out of your system in 7 days, which is why Foundayo is dosed daily; a weekly schedule would leave most of the week uncovered.

The flip side of a short half-life is a fast reset. Where a stopped injection tapers over a month or more, a stopped daily pill is largely gone within days.

Steady state is the point where each new dose only replaces what the body cleared since the last one, so levels stop climbing. The Zepbound label states tirzepatide reaches steady state after 4 weeks of once-weekly dosing. Semaglutide's longer half-life stretches that to about 5 weeks, and Foundayo's short one compresses it to about 8 days.

This is the number behind two common experiences. The first weeks on a weekly injection feel weaker than the label average partly because levels are still climbing: a week after the first tirzepatide dose you are carrying roughly 60% of the eventual steady trough. And every dose increase restarts the same climb at the new height, which is why escalation steps are spaced about a month apart. The “Building up” view in the calculator above shows the climb for your dose.

The missed-dose rules in each label are the half-life story in miniature. The Zepbound and Mounjaro labels allow a missed injection to be taken up to 4 days (96 hours) late, and to be skipped after that; Ozempic's label allows 5 days, and Trulicity's says to take it as soon as possible if at least 3 days (72 hours) remain before the next scheduled dose. The Wegovy label uses a 48-hour rule keyed to the next dose. The daily forms barely look back at all: the tablets say to skip a missed day, and the Saxenda and Victoza labels say to simply resume the once-daily schedule with the next dose.

The logic is visible in the calculator above: a weekly injection still has roughly half its steady level present a week later, so a day or two of delay lands on a meaningful base. These are the labels' instructions to prescribers, not our advice; if you have missed a dose, your own label and prescriber are the authority.

The curve is a standard one-compartment model: absorption at the rate implied by each label's time-to-peak, elimination at the label half-life, and a regular dosing schedule at the label interval. The “Building up” view sums the doses from day 0; the “After stopping” view decays from steady state, with “effectively cleared” drawn at 5% of the steady peak, roughly four to five half-lives.

The milligrams shown are estimated medication in the body after absorption: the dose, multiplied by the absolute bioavailability each label reports (80% for subcutaneous tirzepatide, 89% for subcutaneous semaglutide, approximately 55% for liraglutide, 47% for dulaglutide at maintenance doses, 77% for oral orforglipron, and only 0.4% to 1% for the semaglutide tablets, where the midpoint 0.7% is used), multiplied by the modeled remaining fraction. It is not a blood concentration, and the tablet figures carry the most uncertainty because their absorption range is wide, which is why they display with a tilde. Because these medications behave proportionally, the dose changes only the scale of the axis, never the shape or the timeline.

What the model leaves out: individual variation (label half-lives are medians), the difference between blood level and appetite effect (which fades on its own timetable), and any personal factors your prescriber would weigh. This is an educational reference, not a stopping, switching, or titration planner: decisions about starting, stopping, switching, or restarting belong with your prescriber.

The GlucoPal app's estimated medication levels chart runs this continuously against your real dose history, so the curve reflects the doses you actually took, on the days you actually took them.