About this page

This page is for people who have been prescribed semaglutide and need to calculate the volume to draw. The calculator above does the math. The content below explains how to use it correctly and cites the FDA-approved labels for the branded products. Semaglutide is FDA-approved as Ozempic for type 2 diabetes, as Wegovy for chronic weight management, and as Rybelsus as an oral formulation for type 2 diabetes.¹²

About semaglutide

Semaglutide is a GLP-1 receptor agonist developed by Novo Nordisk. The FDA approved Ozempic in December 2017 for type 2 diabetes, Rybelsus (oral semaglutide) in September 2019 for type 2 diabetes, and Wegovy in June 2021 for chronic weight management in adults with obesity or overweight with at least one weight-related comorbidity. Wegovy approval was later extended to additional indications and to adolescents.¹²

In branded form, Ozempic and Wegovy ship as prefilled pen injectors with no reconstitution required. Rybelsus is an oral tablet. Compounded semaglutide, prescribed by some telehealth providers, is typically dispensed as a lyophilized powder in a multi-dose vial that requires reconstitution with bacteriostatic water before use. The calculator on this page is for the compounded injectable form.

The FDA-approved dosing ladder

The Wegovy label specifies a titration schedule starting at 0.25 mg administered subcutaneously once weekly for 4 weeks. The dose is then increased to 0.5 mg once weekly for 4 weeks, then 1 mg once weekly for 4 weeks, then 1.7 mg once weekly for 4 weeks, and finally to the maintenance dose of 2.4 mg once weekly.¹

The Ozempic label specifies a different titration schedule. The starting dose is 0.25 mg once weekly for 4 weeks, followed by 0.5 mg once weekly. After at least 4 weeks at 0.5 mg, the dose may be increased to 1 mg once weekly for additional glycemic control. The Ozempic label also permits increases to 2 mg once weekly for further glycemic control after at least 4 weeks at 1 mg.²

The two labels reflect the different therapeutic targets — glycemic control for Ozempic, weight management for Wegovy — and the dose ranges are not interchangeable. The labels are the authoritative reference for dosing decisions; this page restates them for context and does not provide an independent dosing schedule. If your prescription differs from the FDA label, your prescriber has reasons that take precedence over the label’s general guidance.

Reconstitution math for compounded semaglutide

Compounded semaglutide vials are commonly dispensed in total mg quantities of 2.5 mg, 5 mg, or 10 mg, though pharmacies vary. The bacteriostatic water volume used for reconstitution depends on the pharmacy and the intended dosing range.

The math is the same as for any reconstitution:

Concentration = vial mg ÷ water mL
Volume to draw = target dose mg ÷ concentration
Units = volume mL × syringe scale (100 for U-100, 40 for U-40)

Example calculation (not a recommendation): If your prescription is for 0.25 mg weekly and your pharmacy provides a 5 mg vial reconstituted with 2 mL of bacteriostatic water, the calculator computes a concentration of 2.5 mg/mL. A 0.25 mg dose at that concentration requires a 0.1 mL draw, which reads as 10 units on a U-100 syringe.

Second example (not a recommendation): If your prescription is for 1 mg weekly and your pharmacy provides a 10 mg vial reconstituted with 2 mL of bacteriostatic water, the calculator computes a concentration of 5 mg/mL. A 1 mg dose at that concentration requires a 0.2 mL draw, which reads as 20 units on a U-100 syringe.

Semaglutide doses span more than an order of magnitude across the FDA-approved range, so draw volumes at lower doses can be small. If your prescribed dose calculates to a sub-unit draw on a standard U-100 syringe, consider whether your reconstitution concentration is too high for accurate measurement. The main calculator discussion of U-100 versus U-40 covers this in more detail.

Branded versus compounded

Branded semaglutide — Ozempic and Wegovy — ships in prefilled pens that handle dose delivery internally. Rybelsus is an oral tablet. Users do not need to reconstitute, calculate volume, or measure with a syringe for the branded forms. The calculator on this page does not apply to branded pens or to Rybelsus.

Compounded semaglutide is prescribed by some telehealth providers when branded products are unavailable, when insurance does not cover the branded form, or when a specific dose is needed that the branded pens do not offer. Compounded products may come from 503A pharmacies (patient-specific compounds prepared on receipt of a prescription) or from 503B outsourcing facilities (larger-scale sterile compounding under FDA registration). The regulatory framework for each pharmacy type differs.

Verify with your prescriber and pharmacy that the source of your medication is appropriate for your situation. This page makes no recommendation between branded and compounded forms.

Beyond-use date considerations

Reconstituted semaglutide is constrained by the same two clocks as any reconstituted peptide.

Bacteriostatic water has a 28-day window after first puncture under USP standards.³ The benzyl alcohol preservative is considered effective against microbial growth for up to 28 days following the first needle entry, and the bottle should be discarded after that point.

Semaglutide stability in solution after reconstitution is determined by the compounding pharmacy and depends on the formulation, storage conditions, and the pharmacy’s validation studies. The branded Ozempic and Wegovy products are not designed for reconstitution by end users, so the published stability data for those products does not translate to compounded vials. The pharmacy’s BUD, if specified, is the authoritative reference.

Track three dates: the bacteriostatic water first-puncture date, the reconstitution date, and any pharmacy-specified BUD. The earliest is your effective BUD. The longer explanation of how these windows interact is in The 28-day rule for bacteriostatic water.

Math, not medical advice

Joust doesn’t recommend doses, prescribe protocols, or claim therapeutic benefits. This page is a calculator, not a prescription. Your prescriber determined your dose and your titration schedule. If those don’t match what your label or pharmacy instructions say, contact them directly.

The calculator’s outputs are correct for the inputs given. The correctness of the inputs is your responsibility. The labels cited on this page describe FDA-approved dosing for the branded products and do not constitute medical advice for any individual.

When to talk to your prescriber

Contact your prescriber if:

Your prescribed dose has changed
You have missed doses or experienced side effects
You are switching from branded to compounded semaglutide or vice versa
You are receiving compounded product from a new pharmacy with a different formulation
The calculator output does not match the instructions on your pharmacy paperwork
You experience symptoms that may be related to the medication

For escalation timing, dose adjustments, and any medical concerns, your prescriber’s guidance applies. The FDA labels referenced on this page describe general dosing intervals but do not address individual circumstances.

References

U.S. Food and Drug Administration. Wegovy (semaglutide) Prescribing Information. Novo Nordisk. ↩ ↩² ↩³
U.S. Food and Drug Administration. Ozempic (semaglutide) Prescribing Information. Novo Nordisk. ↩ ↩² ↩³
United States Pharmacopeial Convention. USP General Chapter <797>: Pharmaceutical Compounding — Sterile Preparations. Establishes maximum beyond-use dates for multi-dose preserved sterile containers, including the 28-day window for bacteriostatic water after first puncture. ↩