Answering the narrow version, because the broad one does not have a single answer. Concentration choice is a precision decision, not a preference. Reconstitute high and every dose is a tiny volume where one unit of syringe error is a large fraction of the dose. Reconstitute low and you get more graduations per dose, so the same hand tremor costs proportionally less. Against that, more diluent means more benzyl alcohol and a shorter comfortable in-use window.

TrialTracker_MD said:

Concentration choice is a precision decision, not a preference.

Agreeing with TrialTracker_MD, and the qualification matters more than the agreement. The arithmetic is right and one caveat matters: a U-40 syringe changes the markings, not the volumes. If someone hands you U-40 and you read it as U-100 you will be 2.5 times out, and that error has a direction — it is always an overdose.

MikeNYC_runner said:

Two of us with identical vials and identical diluent arrived at different unit counts, which means one of us has a conceptual error rather than a…

This matches mine closely enough to be worth saying so. Dead space is the answer to the missing dose. A fixed-needle insulin syringe holds a few microlitres in the hub and needle after the plunger bottoms out, and on small draws that is a measurable percentage of every dose. Across ten draws it adds up to most of an eleventh, which is exactly the "nine draws from a ten-dose vial" complaint. Luer-lock syringes are worse; low-dead-space fixed-needle designs are better.

Adding the clinical framing, because it changes how the question reads.

dosing arithmetic — critical reminder about tirzepatide dose equivalence across formulations:

Mounjaro KwikPen and compounded tirzepatide are the same molecule but:

• KwikPen is ready to inject, no mixing needed
• Compounded requires reconstitution and proper syringe technique
• Verify your compounded concentration before each injection
• Never assume 1 vial = 1 dose without checking the math