Retatrutide Dosage & Reconstitution Calculator

This calculator does one job well. You enter your vial size in milligrams, the amount of bacteriostatic (BAC) water you added, and the target dose you are planning. It returns the concentration, the volume to draw in milliliters, and the matching units on a U-100 insulin syringe.

Retatrutide is an investigational once-weekly peptide that works on three hormone receptors at once: GLP-1, GIP, and glucagon. The calculator does not depend on what retatrutide does in the body. It is pure arithmetic that converts milligrams and milliliters into a number you can read on a syringe.

You only need three numbers. The vial size is printed on the label in milligrams. The BAC water volume is how much you choose to add. The target dose is the amount you want each injection to deliver.

Reconstitution means turning the dry powder in the vial into a liquid you can measure. You do this by adding BAC water. The math behind it is short, and the calculator handles it for you, but it helps to see how it works.

Concentration is the vial size divided by the BAC water you added. A 10 mg vial mixed with 2 mL of BAC water gives 5 mg per mL. The same 10 mg vial mixed with 1 mL gives 10 mg per mL.

Divide your target dose by the concentration. At 5 mg/mL, a 2 mg dose is 0.40 mL. At 10 mg/mL, that same 2 mg dose is only 0.20 mL.

A U-100 insulin syringe has 100 units per 1 mL, so 1 unit equals 0.01 mL. Multiply your draw volume in milliliters by 100 to get units. A 0.40 mL draw is 40 units. A 0.20 mL draw is 20 units.

The preset dropdown above uses the common retatrutide vial setups below. The last column is the units for a 1 mg dose. Multiply it by your target dose in milligrams to get your units.

Many people search for a retatrutide dosage calculator hoping it will tell them what dose to take. This tool does not do that, and on purpose. It converts a dose you enter into units. It does not pick the dose for you.

For context only, the Phase 2 obesity trial published in the New England Journal of Medicine in 2023 studied once-weekly retatrutide at 1 mg, 4 mg, 8 mg, and 12 mg, with gradual escalation over the first weeks to improve tolerability. The highest 12 mg dose produced about 24.2% average body-weight reduction at 48 weeks, compared with 2.1% for placebo. This is reported trial data, not a dosing recommendation.

Search terms like "for weight loss," "female," or "bodybuilding" do not change the math. The calculator output is identical regardless of who is using it or why. Any decision about an actual dose belongs with a qualified clinician. See the semaglutide vs tirzepatide vs retatrutide comparison for how the three compare.

Retatrutide has a half-life of about 6 days, according to the NEJM Phase 2 trial. Half-life is the time it takes for roughly half of the drug to clear from the body. A 6-day half-life is long, which is why trials use one injection per week.

Because the drug clears slowly, levels build up over the first several weeks. Most pharmacology summaries describe steady state at about 4 to 5 weeks at a given dose, with full washout taking roughly 30 days (about five half-lives) after the last dose.

In plain terms: if you inject 5 mg, about 2.5 mg is still present roughly 6 days later. That slow decline is the reason a once-weekly schedule keeps levels fairly steady between injections. This calculator handles the per-injection math; it does not model week-over-week buildup.

In trials, the most common side effects were gastrointestinal: nausea, vomiting, and diarrhea. These were usually mild to moderate and most common during dose escalation, which is the same pattern seen across the GLP-1 drug class.

Phase 3 data reported a skin-sensitivity side effect called dysesthesia, described as tingling or tenderness to touch, in about 20.9% of participants at the highest dose. Longer-term safety is still being studied because the molecule is not yet approved.

No. As of June 2026, retatrutide is not FDA-approved and is not available by prescription. It is an investigational medication from Eli Lilly, still in its Phase 3 TRIUMPH trial program.

Eli Lilly reported its first Phase 3 readout (TRIUMPH-4) in December 2025, showing about 28.7% weight loss at 68 weeks, and a larger pivotal trial (TRIUMPH-1) in May 2026 showing about 28.3% weight loss at 80 weeks in 2,339 participants. A New Drug Application had not been filed at the time of writing.

Because it is not approved, retatrutide sold online is research-use-only material, and quality is not guaranteed. For background on how the FDA has treated unapproved GLP-1 products, see the February 2026 FDA research-use-only update.

The reconstitution math is the same for all three peptides. You divide the vial size by your BAC water volume to get a concentration, then convert your dose to units. Only the typical vial sizes and doses differ.

What sets retatrutide apart is the receptor target, not the math. Semaglutide acts on GLP-1 alone, tirzepatide adds GIP, and retatrutide adds glucagon on top of both. That third receptor is the reason it is called a triple agonist. For the full comparison, see semaglutide vs tirzepatide vs retatrutide.