Tirzepatide Has Six Published Doses. A Calculator Can't Invent a Seventh.

Tirzepatide has exactly six published doses: 2.5, 5, 7.5, 10, 12.5 and 15 milligrams, set by the drug’s label and the trials that tested it. A dosage calculator is useful for exactly one thing: turning one of those six numbers, plus your vial’s concentration, into a syringe reading. It cannot tell you which of the six to use, and it has no authority to hand you a seventh. Most of the time someone spends on a “tirzepatide dosage calculator” should go to understanding the ladder those numbers come from. The division itself is something a browser tab finishes in a tenth of a second.

What a calculator can decide, and what it can’t

A dosage calculator’s job is narrow: convert a target milligram dose and the concentration printed on your vial into a number of units for the syringe. That arithmetic is the full extent of what it decides.

The dose side of that equation is fixed by the drug’s own pivotal trial. Tirzepatide’s SURMOUNT-1 protocol used a 20-week dose-escalation period before participants reached a randomized maintenance dose of 5, 10 or 15 mg weekly.^[1]

Insulin, a peptide hormone most patients already dose by the unit, has a half-life measured in minutes and needs several injections a day to hold blood sugar steady. Tirzepatide sits at the other end of that spectrum. A population pharmacokinetic model built from 19 pooled studies put its half-life close to five days, long enough that once-weekly dosing keeps blood levels from swinging between injections.^[2] That five-day half-life is the reason the drug is dosed weekly rather than daily.

What the randomized SURMOUNT trials measured

SURMOUNT-1 is a phase 3, double-blind, randomized, placebo-controlled trial of 2,539 adults with obesity, the strongest design available for showing a drug caused an effect rather than merely accompanied one.^[1] At the 15 milligram dose, participants lost an average of 20.9 percent of body weight by week 72. The placebo group lost 3.1 percent.^[1]

20.9% average weight loss at week 72 on the 15 mg dose in SURMOUNT-1 PMID 35658024

That gap, measured in a randomized trial, is the real authority on what a given milligram figure does. SURMOUNT-2 ran the same maintenance doses in 938 adults who also had type 2 diabetes, and found a smaller effect: 14.7 percent weight loss at 15 milligrams, against 3.2 percent on placebo.^[3] Diabetes blunting the response to incretin-based drugs is a well-documented pattern in this drug class rather than a flaw in the trial design.

Weight loss at week 72 (% of body weight), by trial and dose

• SURMOUNT-1, 15 mg: 20.9
• SURMOUNT-1, placebo: 3.1
• SURMOUNT-2, 15 mg: 14.7
• SURMOUNT-2, placebo: 3.2

SURMOUNT-1 excluded diabetes. SURMOUNT-2 enrolled only people with type 2 diabetes.

Bottom line: only 5, 10 and 15 mg were ever randomized against placebo in the pivotal obesity trials. The other three numbers on the ladder are a standardized ramp. The trials did not separately test them for effect.

Not every tirzepatide data point comes from a trial built like that. A 24-week real-world study followed 64 adults with obesity who were also being treated for psoriasis, titrated up to 5 milligrams, and found a 10 percent reduction in body weight alongside improvements in several metabolic markers.^[4] That is a genuine finding, but it comes from an observational, non-randomized design.

It can show that weight went down while tirzepatide was being taken. It cannot rule out that diet changes, the concurrent psoriasis treatment, or ordinary regression to the mean did part of the work, the way a placebo arm can. Association is not causation, and a single cohort without randomization should be read as evidence of association rather than proof of effect.

The titration ladder: what’s trial-tested and what’s a standardized ramp

The published ladder has six numbers on it: 2.5, 5, 7.5, 10, 12.5 and 15 milligrams. Only the maintenance doses of 5, 10 and 15 mg were SURMOUNT-1’s randomized, tested endpoints.^[1] The intermediate steps on the way there follow a standardized titration ramp. The trial did not separately test them for their own effect.

Tirzepatide's published dose ladder

Only the maintenance doses were the pivotal trials' randomized endpoints.

A calculator has no opinion about any of this. It takes whatever milligram figure you type in and divides it against your vial’s concentration, which varies by manufacturer and by formulation, to produce a unit count. Converting a specific figure like 2.5 milligrams into units for a given vial size is itself a small piece of arithmetic, covered in detail in our walkthrough of the 2.5 mg conversion. What matters here is the number that goes in before that conversion starts.

• If a calculator, a forum post, or a seller hands you a milligram figure outside the six above, that figure does not correspond to anything a randomized trial has tested.
• The escalation steps were never separately randomized for effect. They are a standardized ramp. The trial did not test them independently.
• Only 5, 10 and 15 mg carry a direct weight-loss result behind them, from the trials described above.

Side effects tied to the escalation steps

SURMOUNT-1 built in a 20-week dose-escalation period before participants reached their randomized maintenance dose, and the trial’s gastrointestinal adverse events clustered during that escalation phase rather than at steady maintenance dosing.^[1] Those adverse events were overwhelmingly gastrointestinal, nausea, diarrhea and vomiting, most of them mild to moderate.^[1]

Discontinuation because of side effects stayed in the single digits: 4.3 percent at the 5 milligram dose, 7.1 percent at 10 milligrams and 6.2 percent at 15 milligrams, against 2.6 percent on placebo.^[1]

• Most gastrointestinal side effects cluster at dose increases rather than at steady maintenance dosing.^[1]
• Discontinuation rates are low but not zero, running roughly two to three times the placebo rate depending on dose.^[1]
• Clinical reviews of the dyspepsia and gastroparesis-like symptoms seen with GLP-1 and GIP agonists recommend slowing the climb for patients with pronounced intolerance, as a management strategy rather than a tested protocol.^[5]

That last point matters for anyone tempted to stretch the published four-week steps into six or eight weeks on their own. It is a reasonable clinical instinct, used by prescribers in practice, but the slower pace itself has not been run through a randomized trial the way the original schedule has.^[5] Adopting it is a judgment call made with a clinician. It is not a documented protocol a calculator can offer.

What a calculator cannot verify about your vial

Run the arithmetic correctly and a calculator will give you the right number of units, provided the concentration you typed in matches what is really in the vial. That is the part no calculator can check.

An FDA pharmacovigilance analysis of more than 81,000 adverse event reports involving GLP-1 class drugs found that compounded versions, including compounded tirzepatide, carried far higher reporting odds for contamination, preparation errors and manufacturing problems than the FDA-approved product: a reporting odds ratio of 19.0 for contamination and 8.5 for compounding or manufacturing issues.^[6] A calculator cannot see any of that. It trusts the label on the vial, and the label is exactly what this analysis found reason to distrust in parts of the compounded supply chain.

The safety signal a calculator cannot see: compounded GLP-1 products showed far higher reporting odds for contamination and manufacturing errors than the FDA-approved drug in an 81,000-report FAERS analysis.^[6]

There is a second thing a calculator cannot tell you: whether a dose is working yet. Tirzepatide’s roughly five-day half-life means a drug level needs about three to four weeks, close to five half-lives by the standard pharmacokinetic rule of thumb, to settle into a new steady state after any dose change.^[2] Judging a dose after one or two injections is judging a signal that has not finished arriving.

What could change the published ladder next

The six-number ladder is not necessarily permanent. SURMOUNT-4 followed 670 participants through a 36-week tirzepatide lead-in, during which they lost an average of 20.9 percent of body weight, then randomized them to continue the drug or switch to placebo for another 52 weeks. Those switched to placebo regained weight, up 14.0 percent from the point of randomization, while those who stayed on tirzepatide kept losing slightly more, down 5.5 percent over the same period.^[7]

That is the strongest evidence yet that the six doses do not confer a lasting metabolic reset. They hold the line for as long as someone keeps taking the drug, and the ladder resets without it.

Separately, the Obesity Medicine Association’s 2023 position statement on compounded peptides, and its 2024 follow-up, describe a supply and regulatory picture that keeps shifting: shortages that pushed people toward compounded alternatives, and a call for clearer rules around what counts as an acceptable substitute for the approved formulation.^[8] Newer dual and triple-hormone agonists now in later-stage development could eventually extend or replace tirzepatide’s ladder altogether. For how tirzepatide’s current numbers stack up against the competition, see our comparison of semaglutide, tirzepatide and retatrutide trial data.

None of that changes what a calculator is good for today. It converts one of six numbers into units, correctly, provided the vial matches its label. The six numbers themselves came from a trial rather than a spreadsheet, and the seventh number nobody has tested is not something any calculator is entitled to invent.

This article is for research and informational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. The peptides discussed here are sold for research use only and are not for human consumption. Nothing in this article constitutes medical advice. Consult a qualified clinician before making changes to a health, training, or supplementation protocol.