GLP-1 Peptide Dose Calculator: Semaglutide, Tirzepatide & Retatrutide

How do you calculate a GLP-1 peptide dose?

GLP-1 dose math has three steps. (1) Concentration = vial mass ÷ BAC water volume. (2) Draw volume = target dose ÷ concentration. (3) Units on a U-100 syringe = draw volume × 100. Example: a 5 mg Semaglutide vial reconstituted with 2 ml BAC water gives 2.5 mg/ml; a 0.25 mg dose is 0.1 ml or 10 units. Peptly computes this live as you slide the BAC water amount, and shows the exact draw mark on a visual syringe.

What you need

• Lyophilized GLP-1 peptide vial (Semaglutide, Tirzepatide, or Retatrutide)
• Bacteriostatic water for injection (BWFI)
• U-100 insulin syringe (standard for human-medicine GLP-1 dosing)
• Isopropyl alcohol swabs
• Peptly iOS app for the math, visual draw, and dose log

The reconstitution math, in one screen

All three steps look like this:

• Concentration = vial mass (mg) ÷ BAC water volume (ml). Example: 10 mg ÷ 3 ml = 3.33 mg/ml.
• Draw volume (ml) = target dose (mg) ÷ concentration (mg/ml). Example: 0.5 mg ÷ 3.33 mg/ml = 0.15 ml.
• Units on a U-100 syringe = draw volume × 100. Example: 0.15 ml × 100 = 15 units.

Peptly does this on every slider tick — no calculator app, no scrap paper, no margin for unit-conversion mistakes.

Step-by-step

1. Confirm the vial mass. Most GLP-1 research vials are sold as lyophilized powder in 5 mg, 10 mg, or 15 mg masses for Semaglutide and Tirzepatide. Read the label and confirm total mass in mg.

2. Pick a BAC water volume. A common starting choice: 2 ml BAC water for a 5 mg vial (concentration 2.5 mg/ml), or 3 ml for a 10 mg vial. The right volume is whichever makes your dose land at 10–50 units on a U-100 syringe. Peptly's slider shows the unit count live as you adjust BAC.

3. Reconstitute slowly. Wipe the rubber stopper with an isopropyl swab. Inject the BAC water down the inside wall of the vial — do not aim at the powder. Swirl gently until dissolved. Never shake.

4. Open Peptly and pick the peptide. Tap Semaglutide, Tirzepatide, or Retatrutide. The peptide-specific profile is preloaded with the standard concentration formulas.

5. Set vial mass and BAC water. Enter the vial mass (e.g., 10 mg) and the BAC water you actually added (e.g., 3 ml). The concentration auto-computes: 10 ÷ 3 = 3.33 mg/ml.

6. Pick your target dose. Use the slider or type the dose in mg or mcg. Standard titration steps for the most common GLP-1 peptides are listed below. Peptly displays the exact U-100 unit count and shows the draw mark on a visual syringe.

7. Save the mix for next time. Tap Save. Future doses from the same vial reload in one tap — no need to re-derive the math.

Semaglutide dose reference (Wegovy / Ozempic titration)

The FDA-approved Semaglutide titration for weight management (Wegovy) is a 4-week step-up to a maintenance dose:

• Weeks 1–4: 0.25 mg once weekly
• Weeks 5–8: 0.5 mg once weekly
• Weeks 9–12: 1.0 mg once weekly
• Weeks 13–16: 1.7 mg once weekly
• Week 17+: 2.4 mg once weekly (maintenance)

Ozempic (Type 2 diabetes) titrates differently: 0.25 mg → 0.5 mg → 1.0 mg → optional 2.0 mg. Peptly lets you slide between these without re-doing the math each week.

Tirzepatide dose reference (Mounjaro / Zepbound titration)

Tirzepatide is dual-receptor (GIP + GLP-1) and titrates more aggressively. FDA-approved Mounjaro / Zepbound schedule:

• Weeks 1–4: 2.5 mg once weekly
• Weeks 5–8: 5 mg once weekly
• Weeks 9–12: 7.5 mg once weekly (optional)
• Weeks 13–16: 10 mg once weekly
• Weeks 17–20: 12.5 mg once weekly (optional)
• Week 21+: 15 mg once weekly (maintenance, max)

A common research-vial choice for Tirzepatide is 10 mg or 15 mg per vial. At 10 mg + 2 ml BAC (5 mg/ml), a 5 mg dose is 1 ml = 100 units — at the upper end of a 100-unit U-100 syringe. Choose a higher BAC volume if you prefer smaller draw volumes per dose.

Retatrutide notes

Retatrutide is a triple-receptor agonist (GIP + GLP-1 + glucagon) still in late-stage clinical research. There is no FDA-approved dosing schedule yet. Published Phase 2 trial doses typically range from 0.5 mg to 12 mg weekly with multi-week titration. Vial masses on the research market commonly come as 5 mg, 10 mg, or 15 mg lyophilized.

Peptly's Retatrutide profile uses the same vial-mass ÷ BAC water math. Choose your concentration so the dose you intend to research lands at a readable unit count on a U-100 syringe. Always consult primary literature for current dose ranges.

Common mistakes

• Mixing up mg and mcg. 1 mg = 1,000 mcg. A 0.25 mg dose is 250 mcg, not 2,500.
• Reading U-40 units on a U-100 syringe. Confirm the syringe label says "U-100" before drawing. Cross-reading causes a 2.5× over- or under-dose.
• Using too little BAC water. A high concentration means your dose lands at 2–3 units, which is unreadable. Add more BAC water to spread the dose across 10–50 units.
• Re-deriving the math every dose. Save the reconstitution mix in Peptly. Future doses reload in one tap.
• Shaking the vial. Swirl or roll between palms. Vigorous shaking can damage peptides.
• Mixing Wegovy and Ozempic schedules. Same molecule, different titration. Peptly lets you pick the schedule explicitly.

Why a calculator beats a spreadsheet

• Visual syringe view. Peptly shows the exact draw mark on a U-100 syringe diagram — you confirm the unit count by eye before pulling.
• Saved mixes. One tap to reload yesterday's reconstitution. No retyping vial + BAC numbers.
• Dose log. Every shot, every site, every cycle stored on-device. No spreadsheet drift.
• Site rotation reminders. Peptly nudges you to alternate injection sites week to week.
• On-device privacy. Nothing leaves your phone. No accounts. No servers.

See also

• Peptide calculator (all profiles)
• BAC water calculator
• Peptide reconstitution math reference
• Peptide dosage reference
• How to reconstitute peptides — step-by-step
• Peptide tracker (injection log)

Primary sources

The titration schedules and weight-loss figures referenced here come from the pivotal clinical trials (New England Journal of Medicine) and the FDA-approved prescribing information. Peptly supplies the reconstitution math — not the clinical data, and not a dose recommendation.

• Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1) — N Engl J Med, 2021.
• Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1) — N Engl J Med, 2022.
• Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial — N Engl J Med, 2023.
• Dose schedules: FDA-approved prescribing information for Wegovy, Ozempic, Mounjaro, and Zepbound (Drugs@FDA).

Frequently asked questions

What is the standard concentration for reconstituted Semaglutide? +

There is no single standard — concentration is whatever vial mass ÷ BAC water volume you choose. A common research convention: 5 mg vial with 2 ml BAC water gives 2.5 mg/ml, where 10 units on a U-100 syringe = 0.25 mg. Peptly computes the exact concentration and draw volume as you pick BAC.

How many units is 0.25 mg of Semaglutide? +

It depends entirely on the vial mass and BAC water you used. Example: at 2.5 mg/ml (5 mg vial + 2 ml BAC), 0.25 mg = 0.1 ml = 10 units on a U-100 syringe. At 5 mg/ml (5 mg vial + 1 ml BAC), 0.25 mg = 0.05 ml = 5 units. Peptly removes this math entirely.

How many units is 5 mg of Tirzepatide? +

Depends on your concentration. Example: at 5 mg/ml (10 mg vial + 2 ml BAC), 5 mg = 1 ml = 100 units on a U-100. At 2.5 mg/ml (10 mg vial + 4 ml BAC), 5 mg = 2 ml = 200 units (you would need two draws). Most research protocols choose a concentration so each dose lands in the 10–50 unit range.

Can I use the same syringe for multiple GLP-1 doses? +

No. Use a new sterile U-100 insulin syringe for each draw. This is a standard injection hygiene rule, not a Peptly recommendation. Reusing syringes risks contamination and dulled needles that increase injection pain.

How long is reconstituted Semaglutide or Tirzepatide stable? +

Stability varies. Most research protocols refrigerate at 2–8 °C and use within 4–6 weeks for Semaglutide and Tirzepatide reconstituted with bacteriostatic water. Consult primary sources or a licensed clinician for stability data specific to your peptide and storage conditions.

What's the difference between U-40 and U-100 syringes for GLP-1 dosing? +

U-100 means 100 units per ml. U-40 means 40 units per ml. The same volume reads as different unit counts on each. Peptly assumes U-100 (the standard human-medicine insulin syringe). Using a U-40 syringe with a U-100 reading will cause a 2.5× overdose. Always confirm your syringe type before drawing.

Why does my draw unit count change when I change BAC water? +

Because concentration changes. More BAC water = lower concentration = larger draw volume for the same dose. Less BAC water = higher concentration = smaller draw. The math is: draw_volume = dose ÷ concentration. The total mass of peptide delivered is the same — only the volume changes.

How does Peptly handle Retatrutide dosing? +

Retatrutide doesn't have an FDA-approved dosing schedule yet — it's a research peptide. Peptly's Retatrutide profile uses the same reconstitution math (vial mass ÷ BAC water = concentration). You set your own target dose in mg or mcg, and Peptly returns the exact draw volume in U-100 units. Always consult primary research literature for dose ranges.