FreePeptideCalc

GLP-1 plotter

The same injection, every week, and the amount in your body still climbs for over a month. This draws that curve from the published half-life, so you can see where it stops climbing.

This is a model of a shape, not a prediction about you. It is a single-compartment first-order elimination model driven by one number — the half-life printed in each compound’s own source document. It assumes each dose appears in the body instantly, which real subcutaneous injections do not; it applies no volume of distribution, so the axis is milligrams in the body rather than a blood concentration; and it knows nothing about you, your weight, your kidneys or your titration. It is not a validated pharmacokinetic simulation, it is not medical advice, and nothing it draws is a dosing recommendation.

Calculator inputs

Set the curve

Choose a compound, interval and horizon; the half-life supplies the shape.

Half-life used: 7 days. About 1 week; steady state after 4–5 weeks, and it stays in circulation about 5–7 weeks after the last dose

Modelled amount in the body
00.130.250.380.595% of plateau03691215weeks since the first injectionmg in bodySingle-compartment first-order model · not a clinical prediction
Modelled accumulation curve. The same figures appear in the injection-by-injection table below.
  • Amount in the body
  • Plateau peak 0.5 mg
  • Plateau trough 0.25 mg
After 1st injection
0.25 mg
Plateau peak
0.5 mg
Accumulation
2×
95% of plateau
4.3 wk

Injection by injection

Same dose every time. The number in the body still rises for weeks, because each injection lands on top of what the last one left behind.

InjectionJust afterShare of plateau
#1week 00.25 mg0.13 mg before the next one50%
#2week 10.38 mg0.19 mg before the next one75%
#3week 20.44 mg0.22 mg before the next one88%
#4week 30.47 mg0.23 mg before the next one94%
#5week 40.48 mg0.24 mg before the next one97%
#6week 50.49 mg0.25 mg before the next one98%
#7week 60.5 mg0.25 mg before the next one99%
#8week 70.5 mg0.25 mg before the next one100%
#9week 80.5 mg0.25 mg before the next one100%
#10week 90.5 mg0.25 mg before the next one100%
#11week 100.5 mg0.25 mg before the next one100%
#12week 110.5 mg0.25 mg before the next one100%

First 12 injections of 17 shown. Everything after this point is flat — that is what a plateau is.

Four or five weeks, whatever the dose

This is the thing about weekly GLP-1 dosing that almost nobody is told, and it falls straight out of one number. If half of a dose is still present when the next one arrives, the second injection leaves you with one and a half doses, the third with one and three quarters, and so on. The total climbs and the gap between successive weeks shrinks, until what leaves between injections equals what goes in.

The plateau is reached after roughly four to five half-lives, and this is where the arithmetic gets counter-intuitive: that timing does not depend on the dose at all. A starting dose and a maximum dose take exactly as long to level off. The Ozempic label states steady-state exposure is achieved following 4 to 5 weeks of once-weekly administration, and the Mounjaro label gives 4 weeks for tirzepatide — both consistent with their one-week and five-day half-lives.

Half-lives this tool runs on

Every figure below is taken from the compound’s own FDA label, or for retatrutide — which has no label anywhere — from the published phase 1 trial. The accumulation column is this model’s own output, not a published measurement.

CompoundHalf-lifeWeekly plateau
SemaglutideFDA label7 days2×of a single dose
TirzepatideFDA label5 days1.61×of a single dose
Dulaglutide (Trulicity)FDA label5 days1.61×of a single dose
LiraglutideFDA label13 hours1×of a single dose
RetatrutideNo approval in any country6 days1.8×of a single dose

Liraglutide is the useful contrast. At about 13 hours it is almost cleared before the next daily injection, so it barely accumulates and plateaus within a couple of days. Everything weekly on this list behaves the opposite way. Each compound’s page carries its regulatory status and the rest of its sourcing.

The one place this model can be checked

A model that cannot be tested is decoration. There is exactly one published number in this cluster that tests this one: the Trulicity label reports that after reaching steady state, the observed accumulation ratio for once-weekly dulaglutide was approximately 1.56. Feed this model nothing but the same label’s five-day half-life and it predicts 1.61 — about 4% high. That agreement is an assertion in the repository’s own test file, so it breaks the build if the maths ever drifts.

Take that for exactly what it is worth. Accumulation between doses depends on the half-life and the interval and on nothing the model omits, which is why it lands close. The same model is visibly wrong in the first day or two after an injection, where it shows an instant spike and the real drug is still being absorbed — the Wegovy label puts semaglutide’s peak 1 to 3 days after the dose, and the Trulicity label puts dulaglutide’s at a median of 48 hours.

What it deliberately omits

Absorption from the subcutaneous depot, a volume of distribution, protein binding, non-linear clearance, renal and hepatic variation, body weight, and titration part-way through a course. Any one of those would change the numbers. None of them change the shape, which is the only thing this page is claiming to show.

Nor does it escalate the dose for you. Real GLP-1 courses step up every four weeks, so a real curve is a staircase of plateaus rather than one. Holding the dose flat is what makes the accumulation visible at all — and for the approved compounds, the titration schedules reproduced from their labels are on the dosing charts.

Common questions

Sources behind every half-life above

Every number on this page comes from one of the documents below. Where no reliable source exists, the page says so instead of filling the gap.

  1. FDA labelFDA / DailyMed· 2026-05
    OZEMPIC (semaglutide) injection — FDA prescribing information
  2. FDA labelFDA· 2026-03
    WEGOVY (semaglutide) injection and tablets — FDA prescribing information
  3. FDA labelFDA / DailyMed· 2026-08
    MOUNJARO (tirzepatide) injection — FDA prescribing information
  4. FDA labelFDA / DailyMed· 2026-08
    ZEPBOUND (tirzepatide) injection — FDA prescribing information
  5. FDA labelFDA / DailyMed
    TRULICITY (dulaglutide) injection — FDA prescribing information
  6. FDA labelFDA / DailyMed
    VICTOZA (liraglutide) injection — FDA prescribing information
  7. FDA labelFDA / DailyMed
    SAXENDA (liraglutide) injection — FDA prescribing information
  8. Published studyThe Lancet· 2022
    Urva S et al. LY3437943, a novel triple GIP/GLP-1/glucagon receptor agonist — phase 1
Also on this site

How long a GLP-1 stays in your system covers the same half-lives from the other direction — what happens after you stop.