GLP-1 half-life calculator
How much semaglutide, tirzepatide or liraglutide is still in your system, how long until it is effectively cleared, and how long a dose change takes to fully land.
These are population averages, not a clearance test. Half-life varies between people with kidney function, body weight and other factors. Use this to understand the shape of the curve and to frame a question, never to decide when it is safe to have a procedure, conceive, or start another medication. Those are decisions for the clinician who knows your history.
Optional. Used to show the estimated amount still circulating.
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How long until it is effectively gone
Pharmacology treats a drug as functionally cleared after about five half-lives, when roughly 97% has been eliminated. That is a convention rather than a hard line, and it says nothing about when the effects stop — appetite and food noise often return well before the last molecule does.
| Medication | Half-life | In days | ~97% cleared | Dosing |
|---|---|---|---|---|
| Semaglutide (Ozempic, Wegovy, Rybelsus) | 165 hours | 6.9 days | 34 days | once weekly |
| Tirzepatide (Mounjaro, Zepbound) | 120 hours | 5.0 days | 25 days | once weekly |
| Liraglutide (Victoza, Saxenda) | 13 hours | 0.5 days | 3 days | once daily |
Approximate elimination half-lives. Individual clearance varies, particularly with reduced kidney function.
Your clearance curve
Each row is one half-life after your last dose.
| Time after last dose | Estimated remaining | What that means |
|---|
Why the same number answers three different questions
1. When will this be out of my system?
Five half-lives is the working answer — about 34 days for semaglutide, 25 days for tirzepatide, under three days for liraglutide. This is the version of the question that comes up before surgery, before pregnancy, and before starting a medication that might interact.
Pregnancy planning is the case where the gap between the drugs matters most, and it is specifically a conversation to have with a prescriber well in advance rather than working from a table on a website.
2. How long until a dose change takes full effect?
The same maths runs in reverse. A weekly drug reaches steady state after roughly four to five half-lives of consistent dosing, so a semaglutide dose increase is still building for four to five weeks. That is one reason titration steps are set four weeks apart, and one reason judging a new dose after ten days tells you very little.
3. I missed a dose — how much is left?
With a half-life around a week, a semaglutide dose missed by a few days leaves most of the previous dose still circulating. That is why the labels allow a delayed dose within a certain window rather than treating it as a restart. What the label actually says depends on the drug and how late you are — the missed dose calculator gives you that rather than a rule of thumb.
What half-life does not tell you
- When the effects stop. Appetite suppression and food noise commonly fade before the drug is cleared. People stopping a GLP-1 often notice hunger returning within one to three weeks, while the molecule is still measurable.
- How fast weight returns. That follows appetite and behaviour, not plasma concentration. In the STEP 1 trial extension, participants regained about two-thirds of lost weight over the year after stopping.
- Your individual clearance. Reduced kidney function, body weight and other medications all shift it. These are averages.
Common questions
- How long does semaglutide stay in your system?
- Semaglutide has an elimination half-life of about one week, so roughly 97% is cleared around five weeks after the final dose. Appetite effects usually fade sooner than that.
- What is the half-life of tirzepatide?
- About 120 hours, or roughly five days. Five half-lives is about 25 days, which is the usual working answer for when it is functionally cleared.
- How long before a dose increase takes full effect?
- Around four to five half-lives of consistent dosing to reach steady state: four to five weeks for semaglutide, three to four for tirzepatide. Judging a new dose in the first week or two mostly measures side effects, not effect.
- Can I use this to decide when to stop before surgery or pregnancy?
- No. Use it to understand the timescale, then have the conversation with your prescriber. Surgical teams also need to know about delayed gastric emptying, which is a separate issue from clearance and matters even when the drug is still on board.
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