How to use the Tirzepatide Reconstitution Calculator

Tab 1: Dose to units

1. Enter the tirzepatide in the vial, in mg, from the label.
2. Enter the bacteriostatic water added, in mL.
3. Pick your syringe size. A 0.5 mL (50-unit) syringe suits most weekly doses.
4. Pick your prescribed weekly dose, or choose “Other amount”.
5. Read the results. You get the unit line, a syringe picture, a table of every dose step for your vial, and how much of the vial you can use within 28 days.

Tab 2: How much water?

1. Enter the vial size, your dose and your syringe.
2. Optionally enter the unit line you want each dose to land on.
3. The table compares water amounts from 0.5 to 5 mL. It shows your dose, what 15 mg would take up, and which options are easy to measure.

Tab 3: Missed dose

1. Choose “A dose I missed” or “Moving my injection to a new day”.
2. Enter the two dates.
3. The tool applies the label’s 4-day and 72-hour rules to your dates.

Tirzepatide mg to units: the formula

Three steps turn a vial and a dose into a line on the syringe.

Worked example: a 10 mg vial with 1 mL of water is 10 mg/mL. A 2.5 mg dose is 2.5 ÷ 10 = 0.25 mL, which is 25 units.

How many units is 2.5 mg of tirzepatide?

It depends on your concentration. At 5 mg/mL it is 50 units. At 10 mg/mL it is 25 units. At 15 mg/mL it is about 16.7 units. At 20 mg/mL it is 12.5 units. At 30 mg/mL it is about 8.3 units. There is no single answer, which is why a units dose from one vial must never be copied to another.

How many units is 5 mg of tirzepatide?

At 10 mg/mL, 5 mg is 50 units. At 15 mg/mL, it is about 33.3 units. At 20 mg/mL, it is 25 units.

Tirzepatide BAC water chart: vial size, water and units

Here is how much bacteriostatic water common tirzepatide vials take, and what each label dose step comes to in units. Values marked “over 1 mL” do not fit in a standard 1 mL insulin syringe.

A pattern worth knowing: 10 mg/mL gives the cleanest numbers. Every 2.5 mg step lands on a multiple of 25 units, and each unit holds exactly 0.1 mg. Concentrations like 15 mg/mL give results such as 33.3 units, which fall between lines and have to be rounded.

The 28-day problem with big tirzepatide vials

Many sites suggest large vials such as 30 mg or 60 mg because they “last longer”. The maths says otherwise. The FDA advises discarding multi-dose GLP-1 vials within 28 days of first use, unless the pharmacy label gives a different date. Tirzepatide is taken once a week. So from one punctured vial, you can use at most 4 doses.

Stretching a vial past its discard date is not a safe way to save money. The preservative in bacteriostatic water does not keep a vial sterile forever, and each puncture is a chance for contamination. Tab 1 shows this for your own vial and dose.

Tirzepatide dose schedule on the approved label

This is the schedule on the Zepbound label. Your prescriber may move more slowly, or stay on one dose longer. Never increase your dose on your own.

The 4-week steps line up with the 28-day vial window. A vial sized for 4 doses of your current step runs out at about the time a dose change could happen.

Missed a tirzepatide dose, or want to change your injection day?

• Missed dose: the label says take it as soon as possible within 4 days (96 hours). If more than 4 days have passed, skip it and take your next dose on your usual day.
• Changing your day: you can move your weekly injection day, as long as the gap between two doses is at least 3 days (72 hours).
• Never double up to make up for a missed dose.

Tab 3 of the calculator checks these rules against your dates.

Brand vs compounded vs “research” tirzepatide

This matters more than any calculation, because the maths is only as good as what is in the vial.

The FDA declared the tirzepatide shortage over on December 19, 2024. Its grace period for compounding copies ended on February 18, 2025 for state-licensed pharmacies, and on March 19, 2025 for outsourcing facilities. A pharmacy can still compound in narrow cases, such as when a prescriber records a real clinical need for a different product.

The FDA has also warned about sellers who label GLP-1 drugs “for research purposes” or “not for human consumption” while giving dosing instructions. These are not checked for purity, strength or sterility. If the vial does not contain what the label says, every number in this calculator will be wrong.

How to reconstitute tirzepatide: general steps

Follow your pharmacy’s instructions first. These are the general clean-technique steps for powdered injectables.

1. Wash your hands and use a clean surface.
2. Let the vials reach room temperature if they were in the fridge.
3. Wipe both stoppers with a fresh alcohol swab and let them dry.
4. Draw the planned water with a new sterile syringe.
5. Add it slowly down the inside wall of the vial, not straight onto the powder.
6. Swirl gently until clear. Do not shake.
7. Check it. If it is cloudy, has particles or will not dissolve, do not use it. Contact your pharmacy.
8. Label the vial with the date mixed, the concentration and the discard date. The “Copy vial label” button gives you the text.

How long does reconstituted tirzepatide last?

Some sites say 30, 45 or even 60 days. The FDA’s advice for multi-dose GLP-1 vials is to discard them within 28 days of first use, unless the label gives a different date. Keep the vial in the fridge unless your pharmacy says otherwise, protect it from light, and do not freeze it.

For comparison, the approved Zepbound single-dose vials can be kept out of the fridge for up to 21 days. That rule is for the brand product only. It does not apply to vials you mix yourself.

Tirzepatide safety warnings

The approved label includes these warnings. They apply to tirzepatide whatever its source.

• Thyroid tumours (boxed warning). Tirzepatide caused thyroid C-cell tumours in rats. It is not known whether it does in people. Do not use it if you or your family have had medullary thyroid cancer or MEN 2.
• Pancreatitis. Severe stomach pain that may spread to the back needs urgent medical help.
• Gallbladder problems and kidney injury from dehydration have been reported. Drink enough fluid, especially if you are vomiting or have diarrhoea.
• Low blood sugar is more likely if you also take insulin or a sulfonylurea.
• Birth control pills. The label advises switching to a non-oral method, or adding a barrier method, for 4 weeks after starting and after each dose increase.
• Surgery or sedation. Tell the team you take tirzepatide, because it slows stomach emptying.
• Pregnancy. Stop tirzepatide when pregnancy is recognised, and speak to your doctor.

This page gives general information only. It is not medical advice and does not endorse any product. Please use tirzepatide only as prescribed, and speak to a qualified healthcare professional about your dose. See our full disclaimer.

Frequently asked questions

More free tools on Find Shilajit

Sources and further reading

1. Eli Lilly and Company. Zepbound (tirzepatide) prescribing information. pi.lilly.com
2. Eli Lilly and Company. Zepbound dosing for healthcare professionals. zepbound.lilly.com
3. US Food and Drug Administration. FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize. fda.gov
4. US Food and Drug Administration. FDA’s concerns with unapproved GLP-1 drugs used for weight loss. Updated September 2026. fda.gov
5. US Food and Drug Administration. FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products. July 2024. fda.gov

Reviewed and updated: September 2026. We update this page when the label or FDA guidance changes.