Semaglutide Reconstitution Calculator
Calculate exactly how many units to inject from your reconstituted semaglutide vial
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.
Frequently Asked Questions
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.
Reconstituted semaglutide with bacteriostatic water is typically stable for 28 days when refrigerated at 36-46°F (2-8°C). Do not freeze reconstituted solution, and discard if the solution becomes cloudy, discolored, or contains particles.
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), while less water means a more concentrated solution (smaller injection volume). For most people, 2 mL per 5 mg vial is the sweet spot.
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.
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.
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.
Sources
- Novo Nordisk. Wegovy (semaglutide) Prescribing Information. FDA. 2023. Link
- 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. Link
- USP <797> Pharmaceutical Compounding — Sterile Preparations. United States Pharmacopeia. 2023. Link
- Allen LV Jr. Basics of Compounding: Reconstituting Powders for Injection. Int J Pharm Compd. 2017;21(5):380-385. Link
Methodology
This calculator uses standard pharmaceutical reconstitution math. Concentration is calculated as the total peptide amount (mg) divided by the volume of bacteriostatic water added (mL), yielding mg/mL. The injection volume is then determined by dividing the desired dose (mg) by the concentration (mg/mL), giving the volume in mL. For insulin syringe units, the volume in mL is multiplied by 100 (since U-100 syringes have 100 units per mL). Doses per vial are calculated by dividing the total peptide amount by the dose per injection.
This calculator assumes complete dissolution of the lyophilized peptide and does not account for dead volume in the syringe or vial (typically 0.02-0.05 mL per injection). Actual injectable doses may be slightly less than calculated due to this dead space.
Semaglutide reconstitution: Concentration = peptide mg / water mL. Injection volume = dose mg / concentration. Syringe units = volume mL x 100 (U-100). Common: 5 mg vial + 2 mL BAC water = 2.5 mg/mL. At 0.25 mg dose = 10 units. Stable 28 days refrigerated. Titration: 0.25 mg weeks 1-4, 0.5 mg weeks 5-8, 1.0 mg weeks 9-12, 1.7 mg weeks 13-16, 2.4 mg maintenance.
What else do you want to know?
Ask Pulse anything.