Free tool
GLP-1 Plotter: Tirzepatide and Semaglutide Levels
The GLP‑1 plotter estimates how a once-weekly dose of tirzepatide (Mounjaro, Zepbound), semaglutide (Ozempic, Wegovy) or investigational retatrutide builds up, as a multiple of one dose. It adds up every weekly dose and halves each one per half-life, which is 5 days for tirzepatide and 1 week for semaglutide (Mounjaro prescribing information, section 12.3; Ozempic prescribing information, section 12.3). The level climbs for 4 to 5 weeks and then levels off.
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Your level
Add your last shot to see your level.
Choose your medicine and add your last shot to see your level now.
How to use this calculator
- Choose tirzepatide, semaglutide or retatrutide.
- Enter your last shot’s date and time, your dose, and since when you have taken it weekly. Add a step-up if your dose changed recently.
- Read your level now, when the low before your next shot comes, and when the level reaches its plateau. The shaded band after each shot is the window in which the label says the peak lands, and inside it the calculator names the window rather than a percentage.
- Try a longer gap between doses, splitting, skipping, stopping or switching from another drug to see the curve change, and keep the link to come back to your own shots.
The 100% line on the chart is the steady-state peak on your current dose. The shape of the curve does not depend on the dose, because the labels report exposure rising in proportion to dose (Zepbound prescribing information, section 12.3). A link to the page keeps the shots you entered.
The model and its formula
The plotter is a one-compartment model with no absorption phase. Each dose starts at 1 and halves once per half-life, and the level at any moment is the sum of what is left of every dose given so far.
The numbers under the chart come from three formulas:
- Share of a dose left when the next is due: r = 0.5 to the power (7 ÷ half-life in days).
- Steady-state level = 1 ÷ (1 − r), as a multiple of a single dose.
- Level after n weekly doses = 1 − r to the power n, as a share of the steady-state level.
For tirzepatide, r = 0.5 to the power (7 ÷ 5) = 0.379. The plateau is 1 ÷ 0.621 = 1.6 times a single dose. After the fourth dose the level is 1 − 0.379 to the power 4 = 98% of it, so it is within 5% by dose 4. For semaglutide, r = 0.5, the plateau is 2.0 times a single dose, and the level reaches 94% after 4 doses and 97% after 5.
The labels report the same timing. Tirzepatide reaches steady state after 4 weeks of weekly doses (Zepbound prescribing information, section 12.3), and semaglutide after 4 to 5 weeks (Ozempic prescribing information, section 12.3).
Half-lives in the plotter
The half-life is the model’s only input. Tirzepatide uses the Mounjaro label figure, semaglutide the Ozempic label figure, and retatrutide a 2022 phase 1b trial, since it has no label (Urva et al., Lancet, 2022). The Zepbound label gives tirzepatide’s half-life as about 5 to 6 days, so the table also shows the 6-day result.
| Medication | Half-life (days) | Left when the next dose is due (%) | Steady-state level (× a single dose) | Within 5% of steady state by |
|---|---|---|---|---|
| Tirzepatide | 5 | 38 | 1.6 | Dose 4 |
| Tirzepatide, upper figure | 6 | 45 | 1.8 | Dose 4 |
| Semaglutide | 7 | 50 | 2.0 | Dose 5 |
| Retatrutide (investigational) | 6 | 45 | 1.8 | Dose 4 |
A 6-day half-life raises the tirzepatide plateau by about 12% (1.8 against 1.6) and does not change when it arrives. A plotter built on a different half-life draws a different curve from the same doses; how to read a GLP‑1 dose curve compares the choices.
In the model, the level just before each weekly dose at steady state is the peak times r, so 38% of the peak for tirzepatide and 50% for semaglutide. Whether that dip explains hunger coming back late in the week is the question in food noise before your next shot.
Earliest week at steady state on the top dose
A new dose restarts the same climb. The earliest week on each top dose is the label minimum of 4 weeks per step, added up (Zepbound prescribing information, section 2.1; Ozempic prescribing information, section 2.2; Wegovy prescribing information, section 2.2). Steady state follows 4 weeks later for tirzepatide and 4 to 5 weeks later for semaglutide.
| Medication and top dose | Earliest week on it | Earliest week at steady state on it |
|---|---|---|
| Zepbound or Mounjaro, 15 mg | 21 | 25 |
| Ozempic, 2 mg | 13 | 17 to 18 |
| Wegovy, 2.4 mg | 17 | 21 to 22 |
| Wegovy, 7.2 mg (after at least 4 weeks on 2.4 mg) | 21 | 25 to 26 |
These weeks are the earliest the labels allow, and the dose titration planner turns them into dates from the day your current dose started. For the first week or two after a step-up, the model’s level is still climbing toward the new plateau; for what that means for symptoms, see why each Zepbound dose increase can bring side effects back.
Log the shots you actually took in Pensday and its free medication-level curve uses your own dates and doses.
After the last dose
Run backwards, the same arithmetic gives the washout: the share left is 0.5 to the power (days since the last dose ÷ half-life in days).
| Days since the last dose | Tirzepatide left (%) | Semaglutide left (%) |
|---|---|---|
| 7 | 38 | 50 |
| 10 | 25 | 37 |
| 14 | 14 | 25 |
| 21 | 5 | 12.5 |
| 28 | 2 | 6 |
| 35 | 1 | 3 |
Semaglutide is in the circulation for about 5 weeks after the last Ozempic dose (Ozempic prescribing information, section 12.3) and about 5 to 7 weeks after the last Wegovy dose (Wegovy prescribing information, section 12.3). For a planned exit, use weaning off semaglutide; for a single late shot, the missed dose guide.
What the model leaves out
- The axis is relative. There is no mg/L on it, and the model knows nothing about your weight or your kidneys.
- Real peaks come later than the model draws them, 1 to 3 days after a semaglutide injection (Ozempic prescribing information, section 12.3) and a median of 24 hours (range 8 to 72) after tirzepatide (Zepbound prescribing information, section 12.3).
- People clear the drug at different rates. The Zepbound label gives a coefficient of variation of about 20% for tirzepatide clearance (Zepbound prescribing information, section 12.3).
- It uses the dates you enter and nothing else; the split dose calculator does the draw arithmetic for a split schedule.
- It models weekly injections only. Wegovy tablets are taken daily and peak about 1 hour after the dose (Wegovy prescribing information, section 12.3).
Questions
Frequently asked questions
Does a higher dose take longer to reach steady state?
No. The time to steady state depends on the half-life, not the dose. Tirzepatide exposure rises in proportion to dose (Zepbound prescribing information, section 12.3), so a bigger dose gives a proportionally higher plateau that still arrives after about 4 weeks.
Why does semaglutide build higher than tirzepatide?
Its half-life is longer, about 1 week against about 5 days (Ozempic prescribing information, section 12.3). Half of each semaglutide dose is left when the next one goes in, against 38% of a tirzepatide dose, so semaglutide levels off at 2.0 times a single dose and tirzepatide at 1.6.
How long does tirzepatide stay in your system after the last shot?
With the plotter’s 5-day half-life (Mounjaro prescribing information, section 12.3), about 14% of the level is left 2 weeks after the last shot and about 1% after 5 weeks. The UK Mounjaro label advises stopping at least 1 month before a planned pregnancy because of the long half-life (Mounjaro SmPC, section 4.6).
Where does the retatrutide curve come from?
Retatrutide has no approved label; Lilly registered pre-approval expanded access for it in June 2026 (ClinicalTrials.gov NCT07629401). The plotter uses the half-life of about 6 days reported in a 12-week phase 1b trial in people with type 2 diabetes (Urva et al., Lancet, 2022). Its trials and approval status are summarized in what retatrutide is and where its trials stand.
Sources
- Mounjaro (tirzepatide) injection, prescribing information, revised August 2026. Eli Lilly and Company, 2026.
- Zepbound (tirzepatide) injection, prescribing information, revised August 2026. Eli Lilly and Company, 2026.
- Ozempic (semaglutide) injection, prescribing information, revised May 2026. Novo Nordisk, 2026.
- Wegovy (semaglutide) injection and tablets, prescribing information, revised June 2026. Novo Nordisk, 2026.
- Mounjaro KwikPen solution for injection in pre-filled pen, Summary of Product Characteristics. Eli Lilly and Company Limited, 2026.
- LY3437943, a novel triple GIP, GLP‑1, and glucagon receptor agonist in people with type 2 diabetes (Urva et al.). The Lancet, 2022.
- Pre-approval Expanded Access of Retatrutide (LY3437943), NCT07629401. ClinicalTrials.gov, Eli Lilly and Company, 2026.
Results are estimates from the published figures in these sources. They are not a measurement or medical advice.
Pensday is a tracking app. It does not give medical advice; talk to your prescriber about your dose.
Pensday is not affiliated with Novo Nordisk or Eli Lilly. Ozempic, Wegovy, Rybelsus, Saxenda and Victoza are trademarks of Novo Nordisk A/S. Mounjaro, Zepbound and Trulicity are trademarks of Eli Lilly and Company.
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