Semaglutide Reconstitution Calculator
Enter your vial strength, the diluent you added and the dose your prescriber specified. You get the draw volume in mL and syringe units on a live syringe, a check for doses that land between marks, a beyond-use warning, and a reverse check that tells you how many milligrams are really in the syringe you just filled.
How do you calculate semaglutide reconstitution?
You need two divisions. First, divide the milligrams of semaglutide in the vial by the millilitres of diluent you added: that is the concentration in mg/mL. Second, divide your prescribed dose in mg by that concentration: that is the volume to draw in mL. On a U-100 insulin syringe each 0.01 mL is one unit, so multiply the volume by 100 to find the number on the barrel.
A common example: a 5 mg vial mixed with 2 mL gives 2.5 mg/mL. A 0.25 mg dose is then 0.1 mL, which reads as 10 units. Change the diluent and every number changes, which is why the concentration on your pharmacy label matters more than any number you find online.
Use the volume your dispensing pharmacy specified. It sets the concentration your dose instructions were written for.
The chips are the standard label steps for Wegovy, shown for convenience. They are not a dose recommendation; enter exactly what your prescriber told you.
Optional: enter the dose you meant to take and the check will show how far off the draw is.
Read the number at the top edge of the plunger stopper that touches the liquid, not the tip of the plunger.
A 1 mL U-100 syringe is usually marked every 2 units; 0.5 mL and 0.3 mL versions are usually marked every 1 unit. Check the marks on the syringe you actually own.
Draw to
10
units on your syringe
0.100 mL of solution
Pharmacist checks on your numbers
Smart mixes: which diluent volume reads best on your syringe?
Same vial, same dose, different amount of diluent. This table tests common volumes against your syringe and ranks how cleanly each one measures. If you want to try a volume, check with your dispensing pharmacy first, then press the button to see it in the calculator.
| Diluent | Concentration | Draw | Reading accuracy |
|---|
Your titration ladder at this concentration
The label schedule for Wegovy steps up every four weeks. This ladder shows what each step would measure on your current mix, so you can spot the step where a syringe runs out of room before you reach it.
| Label step | Dose | Volume | Syringe reading | Barrel used |
|---|
How to read your result
Draw volume
The volume in mL and the matching number on your syringe. Treat the milligram dose as the goal and the syringe reading as the way you reach it.
Reading accuracy
A syringe only has marks at fixed steps. If your dose lands between two marks you would be guessing by eye, so the calculator shows how far the nearest mark is from your dose, as a percentage.
Beyond-use window
A mixed vial is on a clock. With a 28-day label and weekly dosing, four draws fall inside the window. The calculator tells you how much semaglutide would be left over when the window closes.
Reverse check
Already filled a syringe? Switch tabs, enter the units you drew, and see how many milligrams are really inside and how that compares with the dose you intended.
Three worked examples, including one that goes wrong
The formulas are easy. What trips people up is how the answer behaves when the vial, the water and the syringe change. These three examples use the same 0.25 mg starting dose.
5 mg vial + 2 mL
5 ÷ 2 = 2.5 mg/mL.
0.25 ÷ 2.5 = 0.1 mL, which is 10 units. A clean number that sits exactly on a mark.
10 mg vial + 2 mL
10 ÷ 2 = 5 mg/mL.
0.25 ÷ 5 = 0.05 mL, only 5 units. It is exact on paper but small enough that a slip of the plunger is a large share of the dose.
3 mg vial + 1 mL
3 ÷ 1 = 3 mg/mL.
0.25 ÷ 3 = 0.0833 mL, or 8.3 units. On a syringe marked every 2 units the nearest mark is 8 units, which delivers 0.24 mg, about 4% under. Not dangerous, but it is why the Smart mixes table exists.
Notice that the first two examples differ only by the vial strength and the amount of water. A 10 mg vial gives half the units of a 5 mg vial at the same volume of water. For the general version of this arithmetic across other peptides, see the main Peptide Calculator.
Units are not milligrams: the mix-up behind real overdoses
On July 26, 2024 the FDA issued an alert after receiving reports of adverse events, some requiring hospitalization, linked to dosing errors with compounded injectable semaglutide. The agency pointed to patients who were unfamiliar with drawing from a vial and to confusion between milliliters, milligrams and units. In its examples, patients told to draw 5 units drew 50, a provider who meant 5 units wrote 25, and another wrote 20 units when 2 was intended. Some patients took five to twenty times the intended dose.
The root of it is simple. A unit on an insulin syringe is a unit of volume, 0.01 mL on a U-100 syringe, not a unit of semaglutide. The same number of units holds a different amount of drug in a different concentration: 20 units of a 2.5 mg/mL solution is 0.5 mg, while 20 units of a 5 mg/mL solution is 1 mg.
Four habits that catch most errors
- Write three numbers on the vial: total mg, mL of diluent added, and the resulting mg/mL.
- Ask your pharmacist to say your dose out loud in both milligrams and syringe units, once, so the two are linked in your head.
- Use the smallest syringe that holds the volume. The FDA encourages providers and compounders to match the syringe size to the dose.
- Run the reverse check on the number you actually drew before you inject.
If you think you drew or injected too much: do not wait for symptoms. In the United States call Poison Help at 1-800-222-1222 or emergency services, tell them the amount in milligrams, and contact your prescriber. This is general safety information, not an assessment of your situation.
Semaglutide units chart for a U-100 syringe
Every cell is dose ÷ concentration × 100, rounded to one decimal. Readings above 100 units will not fit in a 1 mL syringe. Compare the 5 mg + 2 mL row with the 10 mg + 4 mL row: identical units, different vial and different amount of water, which is exactly why units mean nothing without the concentration.
| Vial + diluent | Concentration | 0.25 mg | 0.5 mg | 1 mg | 1.7 mg | 2.4 mg |
|---|---|---|---|---|---|---|
| 2 mg + 1 mL | 2 mg/mL | 12.5 | 25 | 50 | 85 | over 100 (120) |
| 2 mg + 2 mL | 1 mg/mL | 25 | 50 | 100 | over 100 (170) | over 100 (240) |
| 3 mg + 1 mL | 3 mg/mL | 8.3 | 16.7 | 33.3 | 56.7 | 80 |
| 3 mg + 2 mL | 1.5 mg/mL | 16.7 | 33.3 | 66.7 | over 100 (113) | over 100 (160) |
| 5 mg + 1 mL | 5 mg/mL | 5 | 10 | 20 | 34 | 48 |
| 5 mg + 2 mL | 2.5 mg/mL | 10 | 20 | 40 | 68 | 96 |
| 5 mg + 2.5 mL | 2 mg/mL | 12.5 | 25 | 50 | 85 | over 100 (120) |
| 10 mg + 2 mL | 5 mg/mL | 5 | 10 | 20 | 34 | 48 |
| 10 mg + 4 mL | 2.5 mg/mL | 10 | 20 | 40 | 68 | 96 |
If you want to know how long a given vial lasts at your dose, pair this chart with the Prescription Refill Calculator so you reorder before a titration step runs short.
Choosing how much water: the trade-offs
The amount of diluent does not change how much drug you receive, only how much liquid carries it. That makes it a measuring decision, and it comes with trade-offs worth understanding before you ask your pharmacy about a different volume.
| Choice | What improves | What gets harder |
|---|---|---|
| Less diluent (about 1 mL) | Smaller injection volume; large doses fit in one syringe | Starting doses shrink to a few units that are hard to read |
| Moderate (about 2 mL) | Starting doses land near 10 units; mid doses stay below 50 | The 2.4 mg step approaches the 100-unit limit on a 1 mL syringe |
| More diluent (3 to 5 mL) | Small doses are easy to measure | Large injection volumes; more liquid ageing in the vial |
FDA-approved semaglutide: what the labels actually say
Brand-name semaglutide arrives premixed in pens or as tablets, so none of the approved products need the reconstitution math on this page. The label schedules are still a useful reference for what a standard step looks like.
| Product | Form and use | Labeled dosing pattern | Reconstitution? |
|---|---|---|---|
| Ozempic | Weekly pen for adults with type 2 diabetes | 0.25 mg weekly for 4 weeks (initiation, not a maintenance dose), then 0.5 mg; may increase to 1 mg and then 2 mg after at least 4 weeks at each step. 2 mg is the ceiling. | No, premixed pen |
| Wegovy injection | Weekly pen for chronic weight management and cardiovascular risk reduction | 0.25, 0.5, 1.0, 1.7 then 2.4 mg, stepping up every 4 weeks. Recommended maintenance is 2.4 mg (1.7 mg if 2.4 mg is not tolerated). | No, premixed pen |
| Wegovy HD (7.2 mg) | Weekly single-dose pen for adults with obesity; FDA approved March 19, 2026 | For people who have tolerated 2.4 mg for at least 4 weeks and need additional weight reduction. | No, premixed pen |
| Wegovy pill | Once-daily tablet for weight management and cardiovascular risk reduction; approved December 2025 | 25 mg tablet at maintenance, reached by label titration. Follow the prescribing information. | No, swallowed |
| Rybelsus | Once-daily tablet for type 2 diabetes | Titrated per label. Follow the prescribing information. | No, swallowed |
The tablet products involve no syringe at all. For current labels, check DailyMed, which carries the latest FDA-approved prescribing information.
Compounded semaglutide: the legal picture in 2026
Most pages still describe compounding the way it worked in 2023. The timeline below is what has actually happened, with dates from the FDA and published legal analyses. The same shortage-and-resolution story played out for tirzepatide, which you can follow in our Tirzepatide Dosage Calculator.
2022
Wegovy (March) and Ozempic (August) enter the FDA drug shortage list. While a drug is in shortage, licensed pharmacies may compound versions of it.
July 26, 2024
The FDA issues its alert on dosing errors with compounded injectable semaglutide in multiple-dose vials, citing hospitalizations.
February 21, 2025
The FDA declares the semaglutide shortage resolved. Enforcement discretion for copies of approved products ends on April 22, 2025 for 503A pharmacies and May 22, 2025 for 503B outsourcing facilities.
December 2025
The FDA approves the Wegovy pill, the first oral GLP-1 for weight management, with a US launch in early January 2026.
February to March 2026
The FDA announces it intends to restrict the active ingredients used in mass-marketed compounded GLP-1 drugs and to act on misleading advertising. In March it sends warning letters to dozens of telehealth companies, and on March 19 approves Wegovy HD (7.2 mg).
April 30, 2026
The FDA proposes to exclude semaglutide, tirzepatide and liraglutide from the 503B bulk drug substances list, finding no clinical need for outsourcing facilities to compound them in bulk. The Federal Register notice followed on May 1, 2026. The proposal does not change patient-specific compounding by 503A pharmacies, which remains subject to state law and to the rule against making essentially a copy of an approved drug.
In practice this means brand-name pens are the straightforward route, and compounded vials now sit behind a documented clinical-need standard. Verify the current position on the FDA’s GLP-1 concerns page and ask your state board of pharmacy if you are unsure.
Know what is in your vial: three checks a pharmacist makes
The active ingredient
The FDA notes that some products sold as semaglutide are salt forms such as semaglutide sodium or semaglutide acetate. These are different active ingredients from the one in the approved drugs, and this calculator was not built around them.
The label
A real pharmacy label carries the drug name, total strength, diluent type and volume, resulting concentration, beyond-use date, lot number and the dispensing pharmacy. A missing concentration is a reason to call before you draw anything.
The source
A prescription filled by a state-licensed pharmacy is a different category from a vial marked for research use only. That wording means the maker does not intend it for human use, and it falls outside what this page is designed to support.
The shipment
Injectable GLP-1 drugs need refrigeration. The FDA has received reports of compounded products arriving warm or with too little ice, and advises against using injectables that arrive that way.
Reconstituting a pharmacy-supplied vial, step by step
If your pharmacy supplies freeze-dried powder with written instructions, follow those first. They override anything general on this page. The sequence below reflects standard clean-technique practice.
- Set upWash your hands and clear a clean surface. Gather the vial, the diluent exactly as specified, a new sterile syringe, alcohol swabs and a sharps container.
- InspectCheck names, strengths and expiry dates. Do not use a cracked vial, a diluent that looks cloudy, or powder that looks discolored.
- SwabWipe both rubber stoppers with an alcohol swab and let them dry.
- Draw the diluentPull up the volume your pharmacy specified and clear any large air bubbles.
- Add it gentlyDirect the stream against the inside glass wall of the semaglutide vial, slowly, rather than blasting the powder.
- DissolveLet it sit, then swirl or roll the vial gently. Do not shake. The solution should be clear and colorless; if it is cloudy or has particles, do not use it.
- LabelWrite the date and time mixed, the concentration and the beyond-use date directly on the vial.
- StoreKeep it refrigerated and upright, protected from light, and never frozen. Use a new sterile syringe for every draw and swab the stopper each time.
Storage and beyond-use dates
Unopened brand-name pens belong in the refrigerator, and an Ozempic pen in use can be kept for up to 56 days at room temperature or in the fridge, according to its labeling. A reconstituted vial follows the beyond-use date your pharmacy prints. For multiple-dose vials, USP General Chapter <797> commonly applies a 28-day limit after the vial is first punctured unless the manufacturer or pharmacy specifies otherwise, which is why the calculator defaults to 28 days and lets you change it.
The practical consequence is easy to miss. A 5 mg vial holds 20 doses of 0.25 mg, but weekly dosing uses only four of them in 28 days. The beyond-use check in the calculator shows how much semaglutide would be left over, which is often a reason to ask for a smaller vial.
How semaglutide works, and why it is weekly
Semaglutide is a GLP-1 receptor agonist: an engineered relative of the gut hormone glucagon-like peptide-1, sharing about 94% of its amino-acid sequence with the native human hormone. Two design changes explain the once-weekly schedule. A substitution at position 8 makes it resistant to the DPP-4 enzyme that destroys natural GLP-1 within minutes, and a fatty-acid side chain lets it bind albumin in the blood, which slows clearance and gives a half-life of roughly one week.
Activating GLP-1 receptors lowers blood glucose in a glucose-dependent way, slows gastric emptying and acts on appetite regulation in the brain. Newer agents add more targets: tirzepatide activates both GIP and GLP-1 receptors, and retatrutide adds glucagon receptor activity, which you can explore in our Retatrutide Dosage Calculator.
What the major trials found
In the STEP 1 trial of 1,961 adults with overweight or obesity and without diabetes, semaglutide 2.4 mg weekly produced a mean weight change of about 14.9%, against 2.4% with placebo, at 68 weeks. In the SUSTAIN-6 trial in adults with type 2 diabetes at high cardiovascular risk, semaglutide reduced major cardiovascular events with a hazard ratio of 0.74. The STEP UP program supporting Wegovy HD reported a mean weight loss of 20.7% at 7.2 mg versus 17.5% at 2.4 mg in the efficacy analysis.
Side effects and safety, the way a pharmacist counsels them
The most common effects are gastrointestinal: nausea, vomiting, diarrhea and constipation, usually most noticeable after a dose increase, which is why the label steps up slowly. Semaglutide carries a boxed warning for thyroid C-cell tumors seen in rodents, and it should not be used by anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. Pancreatitis, gallbladder problems, dehydration affecting the kidneys, and low blood sugar when combined with insulin or sulfonylureas are also on the label. Tell your care team you take it before any procedure that involves sedation or anesthesia.
None of that is a reason to avoid a prescribed medicine, but it is a reason to measure it carefully and to report symptoms early. You can report problems with any medicine to the FDA through MedWatch.
What I say to people who ask me for help with a vial
I am a pharmacist, and the conversation I have most often about injectables is not about the drug at all. It is about arithmetic and measuring. These are the points I keep coming back to.
Start from the label, not a forum. The concentration your pharmacy printed is the one your dose instructions were written for. If you change the water without changing the instructions, the unit counts you were given stop meaning what they meant.
A tidy number is not the goal; a measurable one is. 12.5 units sounds neat, but on a syringe marked every 2 units you are guessing between 12 and 14. If a mix lands between marks, ask your pharmacy whether a different volume is acceptable rather than eyeballing it.
Small draws are where mistakes live. Below about 5 units a tiny movement of the plunger is a big slice of the dose. That is the situation the FDA’s 5-unit versus 50-unit example describes.
Check your draw backwards. Before injecting, look at the barrel and ask how many milligrams that is. If the answer is not your dose, stop and call.
A vial that holds twenty doses does not last twenty weeks. Once it is mixed, the beyond-use date decides, not the arithmetic.
This calculator is a second pair of eyes, not a prescriber. When a number looks wrong, the right move is a phone call to the pharmacy that dispensed it.
Semaglutide reconstitution FAQ
Wipe both vial stoppers with alcohol, draw the volume of bacteriostatic water your pharmacy specified, inject it slowly against the glass wall of the semaglutide vial, and swirl gently until clear. Never shake. Then divide the vial’s milligrams by the millilitres added to get the concentration, and use the calculator above for your draw volume. Always follow the volume and instructions on your pharmacy label.
There is no single correct volume; the amount you add simply sets the concentration. Two millilitres gives 2.5 mg/mL, so 0.25 mg is 10 units, and 1 mL gives 5 mg/mL, so 0.25 mg is 5 units. Use the volume your dispensing pharmacy specifies, because your dose instructions were written for that concentration.
It depends on the concentration. At 2.5 mg/mL (a 5 mg vial plus 2 mL), 0.25 mg is 0.1 mL, or 10 units on a U-100 syringe. At 5 mg/mL it is 5 units, and at 2 mg/mL it is 12.5 units. Enter your own vial and diluent in the calculator for an exact figure.
At 2.5 mg/mL, 0.5 mg is 20 units and 1 mg is 40 units on a U-100 syringe. At 5 mg/mL they are 10 and 20 units. The units chart shows nine common vial and diluent combinations side by side.
Divide the dose in milligrams by the concentration in mg/mL. A 0.5 mg dose from a 2.5 mg/mL solution is 0.5 ÷ 2.5 = 0.2 mL. Multiply by 100 to read it as units on a U-100 insulin syringe, which gives 20 units.
Milligrams and micrograms measure the amount of drug, and 1 mg equals 1,000 mcg. Millilitres measure volume. Units on an insulin syringe are only volume markings, where 1 unit equals 0.01 mL on a U-100 syringe. Units tell you how much drug you have only when you also know the concentration.
Use the beyond-use date your dispensing pharmacy prints on the label. For multiple-dose vials, USP General Chapter 797 commonly applies a 28-day limit after first puncture unless the manufacturer or pharmacy specifies otherwise. Keep the vial refrigerated, protected from light and never frozen.
Bacteriostatic water contains 0.9% benzyl alcohol, a preservative that makes a vial suitable for multiple doses. Sterile water has no preservative, so a vial mixed with it is generally treated as single-use. Use whichever diluent your pharmacy specified. Benzyl alcohol is not appropriate for newborns.
Almost always a unit mix-up. A 0.25 mg dose is 250 mcg, and entering 0.25 as micrograms or 250 as milligrams changes the answer by a factor of 1,000. This calculator has mg and mcg toggles and flags doses that look implausible.
Use the smallest syringe that holds the volume so the marks are as fine as possible: a 0.3 mL U-100 syringe for volumes under 0.3 mL, a 0.5 mL syringe up to 0.5 mL, and a 1 mL syringe above that. The FDA encourages providers and compounders to supply a syringe size that matches the dose, so ask your pharmacist to confirm.
Both contain semaglutide from Novo Nordisk. Ozempic is approved for adults with type 2 diabetes and tops out at 2 mg weekly. Wegovy is approved for chronic weight management and cardiovascular risk reduction, with a 2.4 mg maintenance dose and, since March 2026, a 7.2 mg Wegovy HD option. Neither needs reconstitution because the pens arrive premixed.
Brand-name semaglutide is FDA-approved. The FDA declared the shortage over on February 21, 2025, so pharmacies can no longer compound essentially copies of approved products on shortage grounds. Patient-specific compounding by a licensed 503A pharmacy remains possible where a documented clinical need exists, and in April 2026 the FDA proposed keeping semaglutide off the 503B bulks list. Check the FDA’s pages and your state board for the current position.
That wording means the maker does not intend the product for human use and it has not been dispensed under a prescription. The FDA has warned about counterfeit and unapproved GLP-1 products, including salt forms such as semaglutide sodium and acetate that are different active ingredients from approved drugs. Speak to a licensed prescriber and pharmacist before using any such product.
Do not wait for symptoms. In the United States call Poison Help at 1-800-222-1222 or emergency services, tell them the amount in milligrams if you can work it out (the reverse check does this), and contact your prescriber. The FDA has received reports of hospitalization after semaglutide dosing errors.
No. It does arithmetic with the numbers you enter and flags results that look unusual. It never chooses a dose, product or schedule. Those decisions belong to your prescriber and your dispensing pharmacist.
Related peptide calculators
Each calculator below uses the same vial-and-syringe logic with its own peptide-specific details. We link them because the habits you build here, writing the concentration down and checking the draw backwards, apply to every one.
About the reviewer
Manzoor Khan, PharmD
Pharmacist. Over 9 years of experience writing about supplements and medications.
I build these calculators because measurement mistakes with injectables are preventable, and most of the tools I found did arithmetic without showing the safety context behind it. Every figure on this page was checked against hand calculations and against the FDA’s own published dosing-error examples, and legal and regulatory statements carry dates so you can see how current they are.
Read more about the author. This page was last reviewed on October 5, 2026 and is reviewed whenever FDA guidance or product labeling changes.
References
- U.S. Food and Drug Administration. FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products. July 26, 2024. fda.gov
- U.S. Food and Drug Administration. FDA’s concerns with unapproved GLP-1 drugs used for weight loss. fda.gov
- U.S. Food and Drug Administration. FDA intends to take action against non-FDA-approved GLP-1 drugs (press announcement, February 2026). fda.gov
- U.S. Food and Drug Administration. FDA approves fourth product under National Priority Voucher program, higher dose semaglutide (Wegovy HD 7.2 mg). March 19, 2026. fda.gov
- National Library of Medicine. DailyMed: current FDA-approved prescribing information for semaglutide products (Ozempic, Wegovy, Rybelsus). dailymed.nlm.nih.gov
- MedlinePlus (National Library of Medicine). Semaglutide injection: drug information. medlineplus.gov
- U.S. Pharmacopeia. General Chapter <797> Pharmaceutical Compounding: Sterile Preparations. usp.org
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384:989-1002. nejm.org
- Marso SP, Bain SC, Consoli A, et al. Semaglutide and cardiovascular outcomes in patients with type 2 diabetes (SUSTAIN-6). N Engl J Med. 2016;375:1834-1844. nejm.org
- Lau J, Bloch P, Schäffer L, et al. Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide. J Med Chem. 2015;58(18):7370-7380. doi.org
- Knudsen LB, Lau J. The discovery and development of liraglutide and semaglutide. Front Endocrinol. 2019;10:155. doi.org
- Federal Register. List of Bulk Drug Substances for Which There Is a Clinical Need Under Section 503B of the FD&C Act (notice of proposal). 91 Fed. Reg. 23431, May 1, 2026. federalregister.gov