Estimated level now
Choose your medication and dose to see the estimate.
An estimate from the doses and published half-lives, not a blood level. Never change a dose or a schedule because of it: ask your prescriber.
Free tools
GLP-1 half-life calculator: Ozempic, Mounjaro and more
Choose your medication, your dose and how many shots you have taken, and the calculator draws an estimate of how much medication is in your body now, how it builds up and how long it takes to clear. It uses each drug's half-life from its US prescribing information. It is an estimate, not a blood test, and it never tells you what dose to take.
How does the calculator estimate the level?
Each shot is absorbed slowly over the first day or two and then cleared at a steady rate. The half-life is how long the body takes to clear half of what is there: about 1 week for semaglutide, about 5 days for tirzepatide and about 13 hours for liraglutide, according to their labels. The calculator draws one curve per shot and adds them up, so a shot taken before the last one is still part of the total.
Three numbers come from the labels for each drug:
| Medication | Half-life on the label | Share of a dose that is absorbed | Peak after a dose |
|---|---|---|---|
| Semaglutide (Ozempic®, Wegovy®) | About 1 week | 89% | 1 to 3 days |
| Tirzepatide (Mounjaro®, Zepbound®) | About 5 days | 80% | 8 to 72 hours |
| Liraglutide (Saxenda®, Victoza®) | About 13 hours | About 55% | 11 hours |
The labels do not give an absorption speed, so the calculator uses one that puts the peak inside the window each label states.
A worked example: semaglutide 1 mg after the last shot
The doses in this example are illustrative. Someone has taken 1 mg of semaglutide every week for 12 weeks and then takes no more. This is what the calculator estimates after that last shot:
| Time after the last shot | Estimated amount | Share of the peak |
|---|---|---|
| 1 day (the peak) | 1.62 mg | 100% |
| 1 week | 0.92 mg | 57% |
| 2 weeks | 0.46 mg | 28% |
| 3 weeks | 0.23 mg | 14% |
| 4 weeks | 0.11 mg | 7% |
| 5 weeks | 0.06 mg | 4% |
| 6 weeks | 0.03 mg | 2% |
The amount roughly halves every week, as a 1-week half-life predicts. It falls below 10% of its peak about 25 days after the last shot and below 3% after about 37 days. That matches the label, which says semaglutide stays in the circulation for about 5 weeks after the last dose.
The peak is higher than one shot because each new dose lands on what is left of the earlier ones. The same 12 shots of tirzepatide 5 mg fall below 3% about 27 days after the last one, because its half-life is shorter.
Why does the level build up over the first weeks?
A weekly shot does not clear completely before the next one, so the level climbs for several weeks before it settles. The labels put that point at 4 to 5 weeks of weekly shots for semaglutide and 4 weeks for tirzepatide. In the calculator, the level just before the sixth weekly semaglutide shot is already within a few percent of where it settles.
A higher dose moves the whole curve up, and each step up starts a new build-up. The labels of the weekly medicines raise the dose in steps at least 4 weeks apart. Your prescriber decides when and whether to change a dose.
What can the estimate not tell you?
- It is not a blood level. Body weight, kidney function and where you inject change how a real person absorbs and clears a medication. The calculator uses the label's averages.
- It does not say how you will feel. Appetite and side effects do not follow the curve exactly, and the labels do not describe a level at which either starts or stops.
- It does not replace your prescriber's instructions. Never change a dose, skip a shot or double up because of an estimate. For a missed dose, follow your label and your prescriber.
- Compounded medications may differ. A compounded product is not the approved drug, and its strength and absorption may not match the label's figures.
Frequently asked questions
How long does semaglutide stay in your system?
About 5 weeks after the last dose, according to the Ozempic label. With a half-life of about 1 week, the amount roughly halves every week, so after five weeks only a few percent of the last peak is left. Wegovy contains the same medicine and the same half-life applies.
How long does tirzepatide stay in your system?
Tirzepatide's half-life is about 5 days. After five half-lives, about 25 days, only a small share is left, and the calculator puts it below 3% of its last peak about 27 days after a final 5 mg shot taken after 12 weeks.
Why is the half-life of liraglutide so much shorter?
Liraglutide is cleared in about 13 hours, which is why Saxenda and Victoza are taken every day rather than every week. A missed daily dose leaves a gap within a day or two, while a weekly medicine fades over weeks.
Is the estimate the same as the app's?
It is the same kind of estimate: one curve per logged dose, added up. In Dose & Lose the curve is drawn from the doses you actually log, at the times you log them.
Sources
- Ozempic (semaglutide) prescribing information, DailyMed: half-life, absorption, steady state and time in the circulation (§ 12.3).
- Mounjaro (tirzepatide) prescribing information, DailyMed: half-life, absorption and steady state (§ 12.3).
- Saxenda (liraglutide) prescribing information, DailyMed: half-life, absorption and time to peak (§ 12.3).
Published by Petros IT Solutions SRL. Read our editorial policy, and send corrections to office@doseandlose.com.