Semaglutide Reconstitution Calculator
Calculate exactly how many units to draw on your insulin syringe for your prescribed dose of compounded semaglutide.
Calculate Your Injection Volume
What Is Semaglutide Reconstitution?
Brand-name Ozempic and Wegovy come pre-filled in pens with fixed concentrations. Compounded semaglutide from compounding pharmacies arrives as lyophilized powder that you reconstitute yourself. The reconstitution process is straightforward but requires accurate math to ensure correct dosing — this calculator does that math for you.
Medical Disclaimer: This tool provides general educational estimates. Always consult your prescribing physician or healthcare provider before making medication changes or interpreting results from population-based models.
Contents
How to Reconstitute Semaglutide Step by Step
Reconstitution Steps
- Clean the vial tops: Wipe the semaglutide vial and BAC water vial with alcohol swabs. Let dry.
- Draw bacteriostatic water: Using a syringe, draw your chosen amount of BAC water (e.g., 2 mL).
- Inject water slowly: Insert the needle into the semaglutide vial and inject water slowly down the side of the vial. Do not spray directly onto the powder.
- Swirl gently: Roll the vial between your palms or swirl very gently. Never shake — this can damage the peptide.
- Wait for dissolution: The powder should dissolve within 1-5 minutes. The solution should be clear and colorless. If cloudy or contains particles, do not use.
- Store properly: Refrigerate at 36-46°F (2-8°C). Reconstituted semaglutide is typically stable for 28 days refrigerated.
Critical Safety Notes
- Use bacteriostatic water only — not sterile water, saline, or tap water. BAC water contains 0.9% benzyl alcohol as a preservative, allowing multi-dose use.
- Never shake the vial — shaking can denature the peptide and reduce potency.
- Use insulin syringes — U-100 insulin syringes (30, 50, or 100 units) provide the precision needed for peptide dosing.
- Discard after 28 days — even if solution remains, reconstituted peptides degrade over time.
- Only use as prescribed — compounded semaglutide should be obtained through a licensed compounding pharmacy with a valid prescription.
How Much Bacteriostatic Water to Add
The amount of water you add is flexible — more water means a more dilute solution (easier to measure), while less water means a more concentrated solution (smaller injection volume). Here are common reconstitution volumes:
| Vial Size | BAC Water | Concentration | 0.25 mg dose | 0.5 mg dose | 1.0 mg dose |
|---|---|---|---|---|---|
| 5 mg | 1 mL | 5.0 mg/mL | 5 units | 10 units | 20 units |
| 5 mg | 2 mL | 2.5 mg/mL | 10 units | 20 units | 40 units |
| 5 mg | 3 mL | 1.67 mg/mL | 15 units | 30 units | 60 units |
| 10 mg | 2 mL | 5.0 mg/mL | 5 units | 10 units | 20 units |
| 10 mg | 3 mL | 3.33 mg/mL | 7.5 units | 15 units | 30 units |
Tip: 2 mL of BAC water per 5 mg vial is the most common reconstitution volume — it provides easy-to-read measurements on standard insulin syringes.
Semaglutide Titration Schedule
The FDA-approved titration schedule for semaglutide (Wegovy) involves gradual dose increases over 16-20 weeks to minimize gastrointestinal side effects:
- Weeks 1-4: 0.25 mg once weekly (starting dose)
- Weeks 5-8: 0.5 mg once weekly
- Weeks 9-12: 1.0 mg once weekly
- Weeks 13-16: 1.7 mg once weekly
- Week 17+: 2.4 mg once weekly (maintenance dose)
Your prescribing physician may modify this schedule based on your tolerance and response. Some patients remain at lower doses if side effects are significant. The titration exists because starting at full dose causes nausea and vomiting in most patients. Each dose increase allows the body to adapt.
Frequently Asked Questions
What is bacteriostatic water and why do I need it?
Bacteriostatic water (BAC water) is sterile water that contains 0.9% benzyl alcohol as a preservative. The benzyl alcohol prevents bacterial growth, making it safe to draw multiple doses from the same vial over 28 days. Regular sterile water lacks this preservative and should only be used for single-dose vials that are discarded immediately after use.
How long does reconstituted semaglutide last?
Reconstituted semaglutide with bacteriostatic water is typically stable for 28 days when refrigerated at 36-46°F (2-8°C). Some compounding pharmacies assign a 30-day beyond-use date. Always follow the specific instructions from your compounding pharmacy. Do not freeze reconstituted solution, and discard if the solution becomes cloudy, discolored, or contains particles.
Does it matter how much water I add?
The total amount of peptide doesn't change regardless of how much water you add — you're just changing the concentration. More water means a more dilute solution (easier to measure small doses precisely), while less water means a more concentrated solution (smaller injection volume). For most people, 2 mL per 5 mg vial is the sweet spot — it provides measurable volumes on standard insulin syringes without requiring large injections.
What type of syringe should I use?
Use U-100 insulin syringes. They come in 3 sizes: 30-unit (0.3 mL), 50-unit (0.5 mL), and 100-unit (1 mL). For most semaglutide doses with standard reconstitution, a 50-unit or 100-unit syringe works well. Use the smallest syringe that fits your dose for the most precise measurement. The needle gauge (typically 29-31G) doesn't affect the calculation — all U-100 syringes measure 100 units per mL.
Can I use this calculator for tirzepatide (Mounjaro)?
Yes. The reconstitution math is identical for all peptides — concentration equals peptide amount divided by water volume. The calculator includes tirzepatide vial presets. Note that tirzepatide follows a different titration schedule than semaglutide (starting at 2.5 mg, increasing to 5, 7.5, 10, 12.5, or 15 mg), so the titration table shown is specific to semaglutide.
What if I accidentally add too much or too little water?
If you add more water than intended, the solution is simply more dilute — you'll need to inject a larger volume for the same dose. Update the water amount in this calculator and recalculate. If you add less water, the solution is more concentrated — inject less volume. The peptide amount doesn't change either way. What you cannot fix: if you accidentally squirt out some of the reconstituted solution, you've lost peptide and should adjust your total vial amount accordingly.
Sources & Methodology
- Novo Nordisk. Wegovy (semaglutide) Prescribing Information. FDA. 2023.
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002.
- USP <797> Pharmaceutical Compounding — Sterile Preparations. United States Pharmacopeia. 2023.
- Allen LV Jr. Basics of Compounding: Reconstituting Powders for Injection. Int J Pharm Compd. 2017;21(5):380-385.
This calculator uses peer-reviewed formulas and clinical guidelines. Results are estimates and should not replace professional medical advice.