Mounjaro is the type-2-diabetes brand of tirzepatide, supplied as fixed-dose prefilled pens — so the pen needs no math. This page explains the Mounjaro dose schedule, then gives you the calculator you need if you are dosing from a compounded tirzepatide vial instead.
Last reviewed against the Mounjaro prescribing information.
What is the Mounjaro dose schedule?
Mounjaro pens are prefilled at a fixed weekly dose; you use the pen for your current step rather than measuring anything. The label's titration begins at the lowest step and increases roughly every four weeks as tolerated.
Tirzepatide schedules climb to higher milligram numbers than semaglutide, but because pens are fixed-dose, the larger numbers never become a measuring problem until you move to a vial.
- Standard weekly steps: 2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg
- 2.5 mg is a starting step for tolerability, not a maintenance dose
- Pens are fixed-dose — no reconstitution or unit math
How is a compounded tirzepatide vial different from a Mounjaro pen?
Compounded tirzepatide comes as a vial, not a metered pen, so you reconstitute and draw it yourself. With tirzepatide's higher milligram doses, the bacteriostatic water volume you choose has a big effect on how many units you draw — which is exactly what the calculator solves.
On Mounjaro pens you do not need the calculator. On a compounded vial dosed to a comparable schedule, the tirzepatide calculator below turns each step into the units to draw.
- Pen = fixed dose, no math
- Compounded vial = you calculate concentration, draw volume, and units
- Higher mg doses make your BAC water choice matter more
Mounjaro calculator: compounded tirzepatide units for each dose step
The Mounjaro pen itself is fixed-dose, so a “Mounjaro calculator” or “Mounjaro dose calculator” is really a compounded tirzepatide calculator: units = dose (mg) ÷ concentration (mg/mL) × 100 on a U-100 syringe.
At 10 mg/mL (for example a 20 mg vial mixed with 2 mL of bacteriostatic water), each Mounjaro step works out as below. Anything over 100 units will not fit a 1 mL syringe: use a stronger vial or split the dose into two draws. Run your own vial in the calculator above.
- 2.5 mg = 0.25 mL = 25 units
- 5 mg = 0.5 mL = 50 units
- 7.5 mg = 0.75 mL = 75 units
- 10 mg = 1.0 mL = 100 units
- 12.5 mg = 1.25 mL = 125 units (more than a 1 mL syringe)
- 15 mg = 1.5 mL = 150 units (more than a 1 mL syringe)
Compounded tirzepatide reference
U-100 units to draw for each common Tirzepatide dose, by vial size, reconstituted with 2 mL of bacteriostatic water. Change the water volume in the calculator above to recompute for your own setup.
| Vial | Concentration | 2.5 mg | 5 mg | 7.5 mg | 10 mg | 12.5 mg |
|---|---|---|---|---|---|---|
| 5 mg | 2.5 mg/mL | 100 u(1 mL) | 200 u(2 mL) | 300 u(3 mL) | 400 u(4 mL) | 500 u(5 mL) |
| 10 mg | 5 mg/mL | 50 u(0.5 mL) | 100 u(1 mL) | 150 u(1.5 mL) | 200 u(2 mL) | 250 u(2.5 mL) |
| 15 mg | 7.5 mg/mL | 33.3 u(0.33 mL) | 66.7 u(0.67 mL) | 100 u(1 mL) | 133.3 u(1.33 mL) | 166.7 u(1.67 mL) |
Swipe the table to see every dose →
Educational reference only — not a dose recommendation. Units assume a U-100 insulin syringe (100 units = 1 mL on U-100). Always confirm against your own vial, diluent, and clinician or pharmacy instructions.
Frequently asked questions
Do I need a calculator for Mounjaro?
What are the Mounjaro dose steps?
Is Mounjaro the same as Zepbound?
Is there a Mounjaro calculator for compounded tirzepatide?
Primary sources
The Mounjaro label for the pen dose schedule, and the FDA's warning on dosing errors with compounded GLP-1 vials. PepSync makes no clinical claims.