Zepbound is the weight-management brand of tirzepatide, supplied as fixed-dose prefilled pens — so the pen itself needs no math. This page explains the Zepbound dose schedule, then gives you the calculator you need if you are dosing from a compounded tirzepatide vial instead.
Last reviewed against the Zepbound prescribing information.
What is the Zepbound dose schedule?
Zepbound pens are prefilled at a fixed weekly dose, so you select the pen for your step rather than measuring. The label's titration starts at the lowest step and increases roughly every four weeks as tolerated, mirroring tirzepatide's diabetes schedule.
Because the pen is fixed-dose, tirzepatide's higher milligram steps only become a measuring task if you switch to a compounded 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 Zepbound pen?
A compounded tirzepatide vial is reconstituted and drawn by hand, unlike a Zepbound pen. Picking a bacteriostatic water volume that keeps your weekly dose on readable syringe units is the main task — and it changes as you titrate up through the schedule.
On Zepbound pens you do not need the calculator. On a compounded vial dosed to a comparable schedule, the tirzepatide calculator below turns each target into the units to draw.
- Pen = fixed dose, no math
- Compounded vial = you calculate the draw and units
- Re-check the units each time you step the dose up
Zepbound calculator: compounded tirzepatide units for each dose step
The Zepbound pen itself is fixed-dose, so a “Zepbound 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 Zepbound 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.
- 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 Zepbound?
What are the Zepbound dose steps?
Is Zepbound the same as Mounjaro?
Is there a Zepbound calculator for compounded tirzepatide?
Primary sources
The Zepbound label for the pen dose schedule, and the FDA's warning on dosing errors with compounded GLP-1 vials. PepSync makes no clinical claims.