Retatrutide Calculator

The retatrutide calculator above turns three numbers into a syringe reading: the milligrams in your vial, the milliliters of bacteriostatic water you added, and your dose in milligrams. For a 10 mg vial mixed with 2 mL, a 2 mg dose is 40 units on a U-100 insulin syringe. It does the arithmetic and nothing else. It can't tell you what dose to take, and it can't tell you what is really in the vial.

How the retatrutide calculator math works

Three steps turn a vial into a syringe reading.

1. Concentration is the vial's milligrams divided by the milliliters of water. A 10 mg vial with 2 mL is 5 mg per mL.
2. Volume is your dose divided by the concentration. 2 mg divided by 5 mg per mL is 0.4 mL.
3. Units are the volume multiplied by 100 on a U-100 syringe. 0.4 mL is 40 units.

The calculator also counts how many full doses the vial holds at that strength, and it warns you when a single draw won't fit in the syringe you picked. U-100 means 100 units to the milliliter, which is the standard insulin scale (MedlinePlus).

Worked examples

These are straight arithmetic, so you can check the calculator against them.

Retatrutide units at the doses Lilly used in its trials

Lilly's Phase 3 trials dosed in milligrams, never in units. In TRIUMPH-1, everyone started at 2 mg and stepped up every 4 weeks: 4 mg through one step at 2 mg, 9 mg through 2, 4 and 6 mg, and 12 mg through 2, 4, 6 and 9 mg (Lilly's TRIUMPH-1 release). The table below converts each of those doses into units at three common strengths. A 10 mg vial in 2 mL or a 20 mg vial in 4 mL makes 5 mg/mL, a 10 mg vial in 1 mL or a 20 mg vial in 2 mL makes 10 mg/mL, and a 20 mg vial in 1 mL makes 20 mg/mL.

*More than a 1 mL U-100 syringe holds (100 units). Our arithmetic from the doses in the TRIUMPH-1 release.

This is a conversion table, not a schedule. What the trials show about each step is on the retatrutide dosage chart and the dosing schedule, and the starting dose page covers the 2 mg first step.

Our read: the strength you mix decides whether a dose fits in one draw. At 5 mg/mL anything from 6 mg up overflows a 1 mL syringe, and at 10 mg/mL only 12 mg does. At 20 mg/mL every trial dose fits, but 2 mg becomes a 10-unit draw where one misread unit is 10% of the dose.

Reading the syringe

Marks differ between syringes. MedlinePlus describes a standard 1 mL syringe with a mark for every unit, and the syringe in our figure marks every 2 units, so count the lines between two printed numbers on your own before the first draw. Smaller 0.3 mL and 0.5 mL syringes have more space per unit, which makes small doses easier to read.

Common mistakes that throw the number off

Most errors come from the syringe or the water.

A U-40 syringe on a U-100 chart. Syringes made for pet insulin are marked at 40 units per milliliter. The Vetsulin label says any syringe other than a U-40 syringe "will result in incorrect dosing." On a U-40 syringe the 20 mark is 0.5 mL, not 0.2 mL, so at 10 mg/mL you'd draw 5 mg instead of 2 mg. Look for U-100 on the barrel or the box. The units page has the full syringe-size table and runs the conversion backwards, from the number on your syringe to milligrams.

The wrong water figure. The calculator needs the water you actually added. If you used 1.5 mL, enter 1.5. A chart for one mix is wrong for any other mix, because the same 20 units holds a different amount of drug in each.

Units mistaken for milligrams or milliliters. In a 2024 alert about compounded semaglutide vials, FDA said confusion between milliliters, milligrams and "units" may have contributed to dosing errors, and that patients drew five to 20 times the intended dose. In several reports people told to draw 5 units drew 50. That is class evidence from another drug, but the syringe arithmetic is the same.

An oversized syringe for a small draw. FDA also flagged syringes far larger than the prescribed volume. The smaller the syringe that holds your draw, the finer the marks, so use the smallest U-100 syringe that fits.

How many doses a vial holds before day 28

FDA recommends that vials with multiple doses of a sterile drug be used within 28 days of first use, because the contamination risk rises after that, and that you discard the vial at 28 days even if medication remains (FDA's page on unapproved GLP-1 drugs). We found no published stability data for retatrutide once it's mixed, so that general limit is the only line there is. The full reasoning is on the reconstitution page, and storage covers the fridge.

On a weekly schedule, 28 days fits about 4 to 5 doses. The table shows whole doses a vial holds at each trial dose, from the same division the calculator does.

Our read: a 30 mg vial holds 15 doses of 2 mg on paper, but only about 5 fit inside 28 days, so roughly two-thirds of it would be thrown away. A low dose from a big vial is where the milligram price misleads. If you're comparing retatrutide for sale listings, divide the price by the milligrams you'd actually use in 28 days, and remember the milligram figure is the seller's claim. For a worked 10 mg case, see the 10 mg vial page.

Start from the syringe instead

If you'd rather pick how many units a dose should read and work out the water from there, the retatrutide reconstitution calculator runs the same math in reverse. To see what trial averages looked like at a given dose and starting weight, the retatrutide weight loss calculator uses published trial figures. The full range of doses is on the retatrutide dosage page.

What this calculator can't tell you

It trusts the label. Australia's TGA tested a vial sold as retatrutide in a September 14, 2026 advisory and found no retatrutide in it, plus undeclared semaglutide at about 8 times the level in approved semaglutide products. A calculator gives a precise units figure for a vial like that, and the figure means nothing.

It also doesn't know the product's legal status. As of October 2026, no approved retatrutide product exists. Lilly last said, on September 29, 2026, that it plans to submit retatrutide to the FDA in the first quarter of 2027 as a Biologics License Application (BLA). On October 2, 2026, the FDA decided that retatrutide is a drug, not a biological product, so an application would need to be filed under section 505 of the Federal Food, Drug, and Cosmetic Act. Lilly's appeal on that question is pending in the Seventh Circuit, and we found no ruling as of October 31, 2026. The practical side is on whether retatrutide is legal and whether it is safe.

Last, it can't pick a dose. In the trials, doses were stepped up every 4 weeks under a study protocol. Outside a trial, each step is a decision for a doctor who knows your history.