Free GLP-1 Reconstitution & Dosing Tool
Retatrutide Dosage Calculator
Calculate retatrutide injection volume in mL, insulin syringe units, weekly dosing schedule, vial duration and reconstitution based on the vial strength and bacteriostatic water you actually use. Educational tool only, not medical advice.
- Free forever
- Based on published Phase 2 dosing
- No sign-up required
- Runs entirely in your browser
Retatrutide Dosage Calculator
Enter your vial strength, the bacteriostatic water you plan to add and your target dose. Everything else is calculated instantly.
Vial strength (mg per vial)
How many milligrams of retatrutide are in one vial before you add any water. Check the label.
Bacteriostatic water added (mL)
The total volume of bacteriostatic or sterile water you draw into the vial. Common choices are 1 mL, 2 mL or 3 mL.
Desired dose per injection (mg)
The milligrams of retatrutide you want in each injection. Do not choose a dose without discussing it with a prescriber.
Injection frequency
How often you plan to inject. Retatrutide has a half-life of about 6 days and once weekly dosing was used in trials.
Syringe type
The syringe you will draw with. U-100 insulin syringes are the most common, 100 units per 1 mL.
Planned treatment length (weeks)
Used to project how much retatrutide the plan will consume and when your vials will run out.
Preferred injection day
Your regular injection day. This anchors the calendar and the next injection date.
Current weight (optional)
Optional. Used only for the weight tracking chart. Never used to recommend a dose.
Goal weight (optional)
Optional.
Draw this much
Units
40u
Volume
0.4mL
Concentration
5mg/mL
2 mg divided by 5 mg/mL equals 0.4 mL, and 1 mL is 100 units, so that is 40 units.
Educational only. Retatrutide is an investigational drug in clinical trials and is not FDA approved. Never dose without a licensed prescriber.
Your Results
Everything below is calculated from your inputs, in your browser.
Estimated drug activity
Vial usage
Estimated remaining medication in your current vial at the end of the plan. You will need approximately 3 vials in total.
Weekly dose table
The plan below assumes you keep the same dose the whole way. If your prescriber steps you up, recalculate at the new dose.
| Week | Dose | Volume (mL) | Units | Cumulative mg | Vial remaining | Date |
|---|---|---|---|---|---|---|
| 1 | 2 mg | 0.4 mL | 40 u | 2 mg | 8 mg | Mon, Aug 10 |
| 2 | 2 mg | 0.4 mL | 40 u | 4 mg | 6 mg | Mon, Aug 17 |
| 3 | 2 mg | 0.4 mL | 40 u | 6 mg | 4 mg | Mon, Aug 24 |
| 4 | 2 mg | 0.4 mL | 40 u | 8 mg | 2 mg | Mon, Aug 31 |
| 5 | 2 mg | 0.4 mL | 40 u | 10 mg | 0 mg | Mon, Sep 7 |
| 6 | 2 mg | 0.4 mL | 40 u | 12 mg | 8 mg | Mon, Sep 14 |
| 7 | 2 mg | 0.4 mL | 40 u | 14 mg | 6 mg | Mon, Sep 21 |
| 8 | 2 mg | 0.4 mL | 40 u | 16 mg | 4 mg | Mon, Sep 28 |
| 9 | 2 mg | 0.4 mL | 40 u | 18 mg | 2 mg | Mon, Oct 5 |
| 10 | 2 mg | 0.4 mL | 40 u | 20 mg | 0 mg | Mon, Oct 12 |
| 11 | 2 mg | 0.4 mL | 40 u | 22 mg | 8 mg | Mon, Oct 19 |
| 12 | 2 mg | 0.4 mL | 40 u | 24 mg | 6 mg | Mon, Oct 26 |
Injection calendar
12 injections scheduled. First on Mon, Aug 10 2026, last on Mon, Oct 26 2026.
Your data is private. Nothing you type here is stored or sent to a server.
Explore the retatrutide hub
The calculator sits at the centre of a small cluster of retatrutide tools and reference pages. Each card below jumps to the section you want.
Retatrutide Reconstitution Calculator
Plan the exact bacteriostatic water to add for the concentration you want.
Retatrutide Plotter
See a modelled retatrutide activity curve week by week across your plan.
Retatrutide Weekly Schedule
Reference weekly ladder from the Phase 2 obesity trial, plus your personal table.
Retatrutide Weight Loss Tracker
Optional current and goal weight input. No projection, no promises.
Semaglutide vs Retatrutide
How retatrutide differs from semaglutide in mechanism and dosing.
Tirzepatide vs Retatrutide
How the tirzepatide ladder compares to the Phase 2 retatrutide ladder.
What does this calculator do?
The retatrutide dosage calculator turns the milligrams your prescriber recommends into a real world draw on a syringe. Enter your vial strength, the bacteriostatic water you plan to add and your target weekly dose, and it returns the concentration in mg/mL, the injection volume in mL, the number of units on a U-100 insulin syringe, how many injections a single vial will cover and how long that will last across your plan.
Retatrutide is dosed in milligrams but drawn in millilitres, so a mid step in the conversion is where most mistakes happen. This calculator collapses that step into one screen and shows the syringe view alongside the number, so you can see the answer instead of trusting the arithmetic.
Everything runs on your device. No dose is stored, no personal information is sent anywhere, and nothing here replaces the exact instructions on your vial label or your prescriber's directions.
Save this page and open it every time you draw. The calculator does not care how many times you use it, and re-checking the units before every injection is the single easiest way to avoid a dosing error.
Retatrutide reference weekly schedule
Retatrutide is not FDA approved and there is no official prescribing information. The most cited dosing ladder comes from the Jastreboff Phase 2 obesity trial in NEJM 2023, which titrated once weekly injections from 2 mg up to 12 mg with 2 or 4 week steps. The table below reflects the highest arm from that study and is the reference used throughout this hub.
In practice, clinicians who prescribe compounded retatrutide vary widely. Some copy the Phase 2 escalation exactly, some start lower at 0.5 mg or 1 mg to build tolerance, and some hold each step for longer than the trial did. This calculator does not choose for you. It only shows the maths of the dose you enter.
| Weeks | Weekly dose | Notes |
|---|---|---|
| 1 to 4 | 2 mg | Initiation, not a therapeutic dose |
| 5 to 8 | 4 mg | First step up |
| 9 to 12 | 8 mg | Second step up |
| 13 onwards | 12 mg | Top dose in the Phase 2 obesity trial |
Retatrutide dose in mg versus mL
Milligrams are how much drug you inject. Millilitres are the volume of liquid that carries it. The bridge between them is concentration, and concentration depends entirely on how much bacteriostatic water you added to the vial.
The formula is short. Concentration in mg/mL equals the vial strength in mg divided by the bacteriostatic water in mL. Injection volume in mL equals your dose in mg divided by that concentration. That is the entire calculation the tool does above, done for you and shown next to a syringe.
| Vial strength | Bacteriostatic water | Concentration |
|---|---|---|
| 5 mg | 1 mL | 5 mg/mL |
| 5 mg | 2 mL | 2.5 mg/mL |
| 10 mg | 1 mL | 10 mg/mL |
| 10 mg | 2 mL | 5 mg/mL |
| 15 mg | 2 mL | 7.5 mg/mL |
| 20 mg | 2 mL | 10 mg/mL |
| 30 mg | 3 mL | 10 mg/mL |
Higher concentrations mean smaller draws, which is convenient but leaves less margin for error. Ask your prescriber which reconstitution they want you to use rather than picking the smallest volume.
Retatrutide dose in insulin syringe units
A U-100 insulin syringe is calibrated so that 100 units equal 1 mL. That means the unit reading is simply the injection volume in mL multiplied by 100. If your calculator result is 0.20 mL, that is 20 units on a U-100 syringe. If it is 0.08 mL, that is 8 units.
The unit conversion is what people usually want to see, because insulin syringes do not have mL markings you can read at a glance. This calculator prints both numbers, so you can double check the volume against the units before you draw.
| Volume drawn | Units (U-100) |
|---|---|
| 0.05 mL | 5 units |
| 0.10 mL | 10 units |
| 0.15 mL | 15 units |
| 0.20 mL | 20 units |
| 0.25 mL | 25 units |
| 0.40 mL | 40 units |
How to reconstitute a retatrutide vial
Reconstitution is the step where dry retatrutide powder becomes an injectable liquid. You draw bacteriostatic water into a syringe, inject it slowly against the inside wall of the vial, and let the powder dissolve without shaking. The volume of water you add sets the concentration, so the number matters more than most people realise.
The calculator above supports the common choices of 0.5 mL, 1 mL, 2 mL, 3 mL and 5 mL, and any custom value. Once you commit to a volume for a given vial, that is the concentration for every dose you draw from it. Change the water and you change the maths.
- Bring both vials to room temperature before opening
- Wipe the top of each vial with an alcohol swab
- Draw the bacteriostatic water into a clean syringe
- Inject slowly down the side of the retatrutide vial, do not spray
- Swirl gently, do not shake, until fully dissolved
- Label the vial with the concentration and the date it was reconstituted
Never rely on memory for the concentration inside a vial. Write it on the label the moment you reconstitute it.
Weekly retatrutide dosing schedule example
Once you commit to a dose and a reconstitution, the weekly schedule is fixed maths. Each injection uses the same volume, so you can count exactly how many injections a single vial will cover and when the next vial needs to be ready. The weekly dose table produced above is your personal version of the schedule below.
Retatrutide has a half life of roughly 6 days. A once weekly cadence lands the next injection while the previous one is still active, which is what lets levels build to steady state over the first 4 weeks. Skipping a week does not just miss one dose, it lowers your average level for the next 2 weeks as well.
| Week | Dose | Volume | Units | Vial remaining |
|---|---|---|---|---|
| 1 | 4 mg | 0.80 mL | 80 units | 6 mg |
| 2 | 4 mg | 0.80 mL | 80 units | 2 mg |
| 3 | 4 mg | 0.80 mL | 80 units | New vial needed |
How long does one retatrutide vial last?
A vial's duration is the total milligrams in the vial divided by the milligrams you draw each week. A 10 mg vial at 2 mg per week lasts 5 weeks. The same vial at 4 mg per week lasts 2 and a half weeks, and at 8 mg per week it lasts a little over one. Higher doses burn through vials faster, so the plan you enter above is also a shopping schedule.
Reconstituted vials are typically kept refrigerated and used within about 30 to 60 days, though this depends on the bacteriostatic water and the pharmacy's instructions. If your vial will still contain retatrutide after that window, the maths will look fine but the vial will not be. Ask your pharmacy how long each vial is good for once mixed.
Retatrutide half-life and estimated drug activity
Retatrutide has an elimination half-life of approximately 6 days, which is what allows once weekly dosing. Each injection stacks on what remains of the previous one, so blood levels climb for roughly 4 weeks after any dose change before settling into a steady weekly rhythm.
The estimated activity curve above is a model of that build-up, calculated from the dose you entered and the published half-life. It is not a blood test, and it cannot tell you whether your dose is right for you. Its practical use is to explain why a new dose can feel underwhelming for the first month, and why washout after your last injection is measured in weeks rather than days.
Common retatrutide dosing mistakes
The most costly dosing mistakes are boring. They come from mixing up units, using the wrong concentration or drawing from a vial you cannot remember reconstituting. The list below is the short version of what to watch for.
- Confusing milligrams with millilitres. Milligrams are the drug, millilitres are the liquid it lives in.
- Using yesterday's concentration on today's vial. Every vial can be reconstituted differently.
- Reading a U-100 syringe as if it were a tuberculin syringe. Units and mL are not interchangeable.
- Adding too much bacteriostatic water. It thins the concentration and turns your dose into a larger draw.
- Not mixing completely before drawing. Undissolved powder means the first doses under, and the last doses over.
- Injecting a dose meant for a different medication. Semaglutide and tirzepatide look identical in a vial.
Retatrutide safety notes
Retatrutide has completed Phase 2 obesity trials and is in Phase 3, but it is not FDA approved. That means there is no official prescribing information, no approved manufacturer for consumer use in most countries, and no legally sold branded product. Any retatrutide currently available outside a clinical trial is compounded or research grade, and it should only be used under a licensed prescriber's supervision.
Side effects reported in trials are similar in shape to other GLP-1 based medications and are usually gastrointestinal. Nausea, vomiting and constipation are common early and after dose increases. Contact a clinician for severe abdominal pain, persistent vomiting, signs of dehydration or any symptoms of a serious allergic reaction. Never adjust your own dose to manage side effects.
On a GLP-1? Save today's plan and see what happens next
This calculator answers what to draw today. Calqulate Vitals logs every retatrutide, semaglutide or tirzepatide injection, plots your drug levels between doses and checks you against published clinical trial data. Free forever.
- Every injection and dose change on one timeline
- Estimated drug activity between doses
- Weight trend and injection reminders
- Doctor-ready PDF reports (Premium)
Related calculators and trackers
Sources and references
This page is built from public clinical guidance and peer-reviewed research. Always confirm decisions with a licensed clinician.
- 1.Jastreboff AM et al. Triple hormone receptor agonist retatrutide for obesity, a Phase 2 trial. NEJM 2023
- 2.Rosenstock J et al. Retatrutide once weekly for adults with type 2 diabetes, a Phase 2 trial. The Lancet 2023
- 3.Eli Lilly retatrutide clinical trial pipeline
- 4.Coskun T et al. LY3437943, a novel triple GIP, GLP-1 and glucagon receptor agonist. Cell Metabolism 2022
- 5.FDA statement on compounded GLP-1 medications and the risk of dosing errors
Frequently Asked Questions
Frequently Asked Questions
Medical Disclaimer: Calqulate Vitals provides educational information based on published clinical trial data. Retatrutide is an investigational drug that is not FDA approved. This tool is not medical advice, does not create a doctor and patient relationship, and must not be used to start, stop or change any medication. Always follow the exact instructions on your vial label and from a licensed prescriber. If you experience severe abdominal pain, persistent vomiting, signs of dehydration or an allergic reaction, seek medical care immediately.
Tool Information
June 2026
Dr. Jaydeep Sanghani
Meet Akabari
Dr. Jaydeep Sanghani
MBBS, MD, DNB(Anaesth.), PDCC(CCM), DrNB(CCM)
AIIMS Bhubaneswar · AIIMS Rishikesh
Critical care specialist and anesthesiologist with advanced training from AIIMS. Reviews health calculators at Calqulate to ensure medical accuracy and evidence-based standards.
About the authors
Meet Akabari
·Co-Founder, Calqulate.net