Calculator

Retatrutide half-life calculator and dose-level plotter

Updated by the GLP Ladder Editorial Team. Editorial policy.

Short answer

Retatrutide's half-life is about 6 days, so ke = ln2 ÷ 6 = 0.1155 per day and 44.5% of the amount present remains a week later. Weekly doses build by R = 1 ÷ (1 − e^(−7ke)) = 1.8033× and reach about 97% of steady state after 5 half-lives (30 days). Modeled estimate, as of Oct 19, 2026.

Published ladders

Trial or label schedules as published, for modeling only.

Dosing tiers (up to 12)

Tier 1

Tier 2

Tier 3

Tier 4

Tier 5

Mark missed doses

Unchecked doses are modeled as not taken.

Peak amount
19.67 mg-eq
Stable window from
Day 126
Stable average
14.64 mg-eq
Accumulation R
1.803×
Retatrutide: modeled relative amount for the Phase 3 12 mg armStep chart of weekly doses (2 mg, 4 mg, 6 mg, 9 mg, 12 mg) above a curve of the modeled amount in the body, peaking at 19.67 mg-equivalents in week 28. Weekly values are in the table below.stable window06.2512.518.7525mg-eq048121620242832weeks from start2 mg4 mg6 mg9 mg12 mg
  • Dose ladder: mg per dose for each tier
  • One tick per dose; an open circle is a missed dose
  • Modeled relative amount in mg-equivalents (F = 1), not plasma concentration
  • Stable window: weekly troughs change by under 5%

How the model works.

Day 190: 19.665 mg-eq modeled. Move the slider or hover the chart for the per-dose breakdown.

Weekly data table
Modeled amount by week, Phase 3 12 mg arm, start Oct 19, 2026 (mg-equivalents)
WeekStartsDose mgPeakTroughAverage
1Oct 19, 202621.78201.287
2Oct 26, 202622.6080.9211.945
3Nov 2, 202622.9781.3312.238
4Nov 9, 202623.1441.5142.368
5Nov 16, 202644.9931.5953.713
6Nov 23, 202645.8572.5534.397
7Nov 30, 202646.2442.9794.701
8Dec 7, 202646.4173.1694.837
9Dec 14, 202668.2663.2546.184
10Dec 21, 202669.1344.2126.869
11Dec 28, 202669.5214.6397.174
12Jan 4, 202769.6944.8297.31
13Jan 11, 2027912.434.9149.3
14Jan 18, 2027913.7146.33310.314
15Jan 25, 2027914.2886.96610.766
16Feb 1, 2027914.5447.24710.967
17Feb 8, 20271217.3157.37312.987
18Feb 15, 20271218.6178.8114.013
19Feb 22, 20271219.1999.4514.471
20Mar 1, 20271219.4589.73514.675
21Mar 8, 20271219.5739.86314.765
22Mar 15, 20271219.6249.91914.806
23Mar 22, 20271219.6479.94414.824
24Mar 29, 20271219.6589.95614.832
25Apr 5, 20271219.6629.96114.835
26Apr 12, 20271219.6649.96314.837
27Apr 19, 20271219.6659.96414.838
28Apr 26, 20271219.6659.96414.838
29May 3, 2027—10.3564.6357.119
30May 10, 2027—4.6132.0653.171
31May 17, 2027—2.0550.921.412
32May 24, 2027—0.9150.410.629

Math, parameters and sources: model card.

How the plotter models levels

Each dose is treated as a one-compartment, first-order absorption curve (the Bateman function), and the curves for every dose are added together. The rate of elimination comes from the half-life (ke = ln2 ÷ t½) and the rate of absorption is solved from the published time to peak. The result is a relative amount in mg-equivalents with bioavailability set to 1, which is why it is useful for comparing schedules and not for reading a blood level.

Model parameters and derived constants (one weekly dose interval, τ = 7 days)
Compoundt½ (days)tmax (h)ke (/day)ka (/day)RLeft after 7 d
Retatrutide6240.1155253.53711.80330.4454
Tirzepatide5240.1386293.31221.61010.3789
Semaglutide7360.0990212.151420.5

Published ladders preloaded

The preset buttons load schedules exactly as published. They are there so you can see what a trial or label schedule looks like on the curve; none of them is a recommendation.

Ladders available in this plotter, with their source
LadderSteps (mg, weekly)Weeks per stepSource
Retatrutide Phase 3 12 mg arm2 → 4 → 6 → 9 → 124Eli Lilly, May 21, 2026
Retatrutide Phase 3 9 mg arm2 → 4 → 6 → 94Eli Lilly, May 21, 2026
Retatrutide Phase 3 4 mg arm2 → 44Eli Lilly, May 21, 2026
Retatrutide Phase 2 12 mg arm2 → 4 → 8 → 124Eli Lilly, hosted on ClinicalTrials.gov, Aug 29, 2022
Retatrutide Phase 2 8 mg arm (2 mg start)2 → 4 → 84Eli Lilly, hosted on ClinicalTrials.gov, Aug 29, 2022
Retatrutide Phase 2 8 mg arm (4 mg start)4 → 84Eli Lilly, hosted on ClinicalTrials.gov, Aug 29, 2022

Reading the stable window

With a fixed weekly dose, each week's lowest point (the trough) rises less than the week before. The plotter shades the "stable window" from the first week in which two consecutive week-over-week trough changes are both under 5%. After any dose increase the climb restarts, so a titration ladder usually reaches its stable window only on the final step. A missed dose shows up as a dip in both the curve and the weekly table.

How to read a dose-level curve (Retatrutide, 1 mg weekly for 10 weeks, modeled)
Annotated modeled curve for weekly retatrutide: first peak, trough, accumulation, stable window and washout, keyed to the list below. 1 2 3 4 5
  1. First peak about 24 hours after the first dose (time to peak).
  2. Trough: the lowest point, just before the next weekly dose.
  3. Accumulation: each dose adds to what is left, so peaks and troughs climb toward about 1.8× a single dose.
  4. Stable window: from about day 28, the weekly trough changes by less than 5% from one week to the next.
  5. Washout: after the last dose the amount halves every 6 days.

Relative amount (mg-equivalents), not a blood level. Model and sources: model card.

Frequently asked questions

What is the half-life of retatrutide?

Phase 1b multiple-ascending-dose study reported a half-life of about 6 days; the Phase 2 protocol summary of single-dose data gives about 5–7 days. The plotter uses 6 days and a time to peak of 24 hours.

How long does retatrutide take to reach steady state?

About 5 half-lives, or roughly 30 days at a constant weekly dose, reaches about 97% of steady state (1 − 2^−5 = 96.9%). Each dose increase restarts that climb toward a new plateau. The plotter marks a "stable window" when the weekly trough changes by less than 5% across two consecutive weeks.

How much retatrutide is left after a week?

By elimination alone, e^(−7 × 0.1155) = 0.4454, so about 44.5% of the amount present at the start of the week remains at its end. That carry-over is why weekly doses accumulate by about 1.8× before levels flatten.

Is the plotter output a blood level?

No. It is a relative amount in mg-equivalents from a one-compartment model with first-order absorption and bioavailability set to 1. Real plasma concentrations depend on body size, absorption site and individual clearance. Use the curve to compare schedules, not to judge your own levels.

Is retatrutide FDA approved?

No. As of Oct 19, 2026 retatrutide is investigational. Lilly reported Phase 3 results in 2026 and said it plans to submit to the FDA in the first quarter of 2027. It is legally available only to participants in Lilly clinical trials.

Sources

  1. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. The Lancet 2022;400(10366):1869-1881 (abstract via PubMed PMID 36354040; doi:10.1016/S0140-6736(22)02033-5), Oct 27, 2022. Accessed Oct 19, 2026.
  2. Study Protocol J1I-MC-GZBF(b) for NCT04881760 (Prot_000.pdf). Eli Lilly and Company, hosted on ClinicalTrials.gov, Aug 29, 2022. Accessed Oct 19, 2026.
  3. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. Eli Lilly and Company (via PR Newswire; also investor.lilly.com), May 21, 2026. Accessed Oct 19, 2026.
  4. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med (abstract via PubMed PMID 42814954; doi:10.1056/NEJMoa2604169), Sep 29, 2026. Accessed Oct 19, 2026.

The curve and figures are a modeled relative amount in the body (mg-equivalents), not a blood level.

Printed from GLP Ladder. To recreate this result, open https://glpladder.com/tools/retatrutide-plotter/

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