Dosage calculator
GLP-1 Reverse Dose Calculator
Your telehealth provider told you to draw a certain number of units on your insulin syringe. This calculator tells you exactly how many milligrams that is, whether it exceeds FDA-approved limits, and which branded dose tier it corresponds to.
Check your vial label. The concentration is printed on every compounded vial.
You are injecting
1mg
Volume drawn
0.400mL
FDA max weekly dose
2.4mg (Wegovy)
Equivalent branded dose
1 mg — Wegovy escalation dose (weeks 9-12)
Quick reference: units → mg at common concentrations
Semaglutide doses at common compounded concentrations.
| Units | @ 2.5 mg/mL | @ 5 mg/mL | @ 10 mg/mL |
|---|---|---|---|
| 5 units | 0.13 mg | 0.25 mg | 0.5 mg |
| 10 units | 0.25 mg | 0.5 mg | 1 mg |
| 15 units | 0.38 mg | 0.75 mg | 1.5 mg |
| 20 units | 0.5 mg | 1 mg | 2 mg |
| 25 units | 0.63 mg | 1.25 mg | 2.5 mg(above max) |
| 30 units | 0.75 mg | 1.5 mg | 3 mg(above max) |
| 40 units | 1 mg | 2 mg | 4 mg(above max) |
| 50 units | 1.25 mg | 2.5 mg(above max) | 5 mg(above max) |
| 60 units | 1.5 mg | 3 mg(above max) | 6 mg(above max) |
| 80 units | 2 mg | 4 mg(above max) | 8 mg(above max) |
| 100 units | 2.5 mg(above max) | 5 mg(above max) | 1 mg(above max) |
How the reverse calculation works
The standard insulin syringe used with compounded GLP-1 vials is a U-100 syringe, meaning 100 units = 1 mL [1]. When you know the number of units you drew and the concentration printed on your vial label (in mg/mL), the milligram dose is:
mg = (units × concentration in mg/mL) ÷ 100
For example, if you drew 40 units from a 2.5 mg/mL semaglutide vial:
mg = (40 × 2.5) ÷ 100 = 1.0 mg
That 1.0 mg corresponds to the Wegovy week 9-12 escalation dose [2]. If the same 40 units were drawn from a 5 mg/mL vial, you would be injecting 2.0 mg — nearly double. This is why verifying the vial concentration is critical.
When to use this tool
- Your provider said “draw to the 25 unit mark” and you want to know what milligram dose that actually is.
- You changed pharmacies and the new vial has a different concentration — you want to verify the old unit count still gives you the same mg dose.
- You want to cross-reference your dose against the FDA-approved Wegovy or Zepbound titration schedule.
FDA maximum weekly doses
The calculator flags any dose that exceeds the FDA-approved maximum weekly dose for the selected drug:
- Semaglutide: 2.4 mg/week (Wegovy maintenance dose) [2]. The Ozempic maximum for type 2 diabetes is 2.0 mg/week [3].
- Tirzepatide: 15 mg/week (Zepbound/Mounjaro maintenance dose) [4, 5].
Exceeding these doses does not necessarily mean the prescription is wrong — some prescribers titrate above the labeled maximum off-label — but it warrants a conversation with your provider.
Important safety disclaimer
This tool performs arithmetic only and does not provide medical advice. Always verify the concentration on your vial label before drawing any dose. If the number on screen does not match what your provider told you, do not inject — call your prescriber or compounding pharmacy first.
Related tools and research
- GLP-1 unit ↔ mg converter — convert in either direction with full lookup tables.
- GLP-1 split dose calculator — split your weekly dose into 2 or 3 smaller injections.
- GLP-1 vial transition calculator — recalculate syringe units when your vial concentration changes.
- GLP-1 dose plotter — visualize how each titration step builds toward steady state.
- GLP-1 reconstitution calculator — calculate BAC water volume for lyophilized vials.
- Compounded semaglutide bioequivalence — what compounding pharmacies are required to test.
References
- 1.Becton, Dickinson and Company (BD). BD Ultra-Fine Insulin Syringes — Product Specifications and U-100 Standard. BD Diabetes Care Product Documentation. 2024. https://www.bd.com/en-us/products/diabetes/diabetes-injection/insulin-syringes
- 2.Novo Nordisk Inc. WEGOVY (semaglutide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215256s026lbl.pdf
- 3.Novo Nordisk Inc. OZEMPIC (semaglutide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/209637s035,209637s037lbl.pdf
- 4.Eli Lilly and Company. ZEPBOUND (tirzepatide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/217806s002lbl.pdf
- 5.Eli Lilly and Company. MOUNJARO (tirzepatide) injection — US Prescribing Information. FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215866s039lbl.pdf
- 6.U.S. Food and Drug Administration. Compounded Drug Products — 503A and 503B Outsourcing Facility Information for Patients. FDA Drug Compounding Resources. 2024. https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers