Tools · Reconstitution
Semaglutide & tirzepatide reconstitution calculator
Turn a compounded vial and a volume of bacteriostatic water into the units to draw — then work the sum backwards, which is the part that actually matters at a low dose: how much water makes your dose land on a number you can read. It also tells you how many doses the vial holds, how many weeks that is, and what you are paying per milligram actually taken.
Read before you use this
This is an educational math tool, not medical advice, and not a recommendation to microdose. Intentional GLP-1 microdosing is off-label and unproven — there are no dedicated randomized trials of sub-therapeutic GLP-1 dosing. Reconstitution volume, storage, beyond-use dating and injection technique must be directed by a licensed clinician and the dispensing pharmacy, whose instructions override anything computed here. Compounded GLP-1s are not FDA-approved products. Confirm the vial strength on the label before you trust a single figure below.
Draw on a U-100 insulin syringe
5units
at 5 mg/mL, which is 10 mg dissolved in 2 mL.
Work backwards: land the dose on a number you can read
This is the calculation that matters most at a low dose, and the forward calculator does not answer it. Pick the mark you want to draw to and this tells you how much bacteriostatic water gets you there.
Add this much water
2.5 mL
0.25 mg × 100 ÷ 10 units
The vial holds the same amount of drug either way — more water means a weaker solution and a bigger volume for the same dose, not more medicine. Check that the volume you land on fits the vial, and follow whatever your prescriber and the compounding pharmacy specify over anything a calculator tells you.
What this vial actually costs you per milligram
No telehealth provider publishes this, because almost none of them publish a vial strength — which is why our price boards rank on pricing structure instead of inventing the number. You are the one person who can compute it, because the vial is in your hand. Optional: leave the cost blank and the rest of the tool still works.
- Doses in this vial
- 40
- 10 mg ÷ 0.25 mg
- Weeks it lasts
- 40wk
- 40 doses ÷ 1/wk
- Cost per dose
- —
- enter a vial cost
- Cost per mg taken
- —
- enter a vial cost
- Cost per week
- —
- enter a vial cost
How it is calculated. Concentration = vial (mg) ÷ water (mL). Units to draw = dose (mg) ÷ concentration × 100, because a U-100 syringe holds 100 units per millilitre. Water for a target unit count = dose (mg) × 100 ÷ units. Doses per vial = vial (mg) ÷ dose (mg). Cost per milligram = vial cost ÷ vial (mg). Worked example: a 10 mg vial in 2 mL is 5 mg/mL, so 0.25 mg is 5 units and the vial holds 40 doses. This is arithmetic, not medical advice, and it is not a recommendation to microdose.
Reconstitution questions
- How much bacteriostatic water should I add to a tirzepatide vial?
- There is no single right answer, because the water does not change how much drug is in the vial — only how concentrated it is and therefore how many syringe units your dose occupies. More water means a weaker solution and a larger, easier-to-read volume for the same dose. The practical approach is to decide what number of units you want to draw and work backwards to the water, which is what the second panel of this calculator does. Follow whatever your prescriber and the compounding pharmacy specify.
- How many units is 0.25 mg of semaglutide?
- It depends entirely on the concentration, which is why the question has no fixed answer. A 10 mg vial reconstituted with 2 mL gives 5 mg/mL, and 0.25 mg of that is 0.05 mL — five units on a U-100 insulin syringe. The same 0.25 mg from a 5 mg vial in 2 mL would be ten units. Always compute it from your own vial and your own water volume rather than copying a number from a chart made for a different vial.
- Why does my microdose come out at only two or three units?
- Because the vial was reconstituted to a concentration meant for full doses. At the low end of a U-100 syringe the gradations are close together, and a half-unit misread on a three-unit dose is a large proportional error. Reconstituting with more bacteriostatic water spreads the same dose across more units without changing the amount of drug, which makes it easier to draw accurately.
- How long should a reconstituted GLP-1 vial last?
- This calculator tells you how many doses your vial contains at your dose, which is the arithmetic. How long it remains suitable to use after reconstitution is a different question, governed by the compounding pharmacy's beyond-use date and storage instructions rather than by the maths — a vial can hold twenty doses and still have a beyond-use date well before you would finish them. Follow the pharmacy's dating and your prescriber's instructions.
The rest of the arithmetic
- Tirzepatide & semaglutide dosage calculator — dose to units, in mcg or mg
- Microdose titration planner — a week-by-week schedule
- How to reconstitute a compounded GLP-1 microdose — the procedure, not the sums
- Splitting a GLP-1 dose — why a partial draw goes wrong
- Cheapest tirzepatide for microdosing — and why no board can publish a cost per mg
Informational only, and not medical advice. This tool performs unit and cost arithmetic; it knows nothing about your health, the specific product in your vial, its beyond-use date, sterility, injection technique or clinical appropriateness. GLP-1 medications are prescription-only after clinician review, compounded GLP-1s are not FDA-approved, and intentional microdosing is off-label with no dedicated clinical trials behind it.