Tirzepatide Calculator:
Reconstitution, Dosage
& Weight Loss Planner
The most complete free tirzepatide calculator available — covering everything from reconstitution (BAC water volume + syringe units) and mg-to-units dosage conversion, to weight loss projections based on SURMOUNT trial data, protein intake for muscle preservation, and half-life tracking. Works for all vial sizes from 5mg to 60mg, and covers both compounded tirzepatide and brand-name Mounjaro and Zepbound.
FatScientist and PeptideIQ only calculate units. We give you 5 complete calculators in one place: reconstitution, dosage conversion, weight loss projection by dose, protein intake for lean mass preservation, and half-life tracking — all with a syringe visual, titration timeline, and step-by-step formulas. Free, no sign-up, no ads.
This calculator is for educational and informational purposes only. Tirzepatide (Mounjaro®, Zepbound®) is an FDA-approved prescription medication. Compounded tirzepatide exists under specific regulatory conditions. This tool does not constitute medical advice. Never adjust your prescribed dosage without consulting your licensed healthcare provider. Injection errors can cause serious harm.
Tirzepatide Calculator
SURMOUNT DataEnter your vial size, BAC water volume, and desired dose. The calculator gives you exact syringe units plus concentration and draw volume.
Total mg in your vial
mL of bacteriostatic water added
Typical: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, 15mg
Already know your concentration? Enter your dose in mg and concentration in mg/mL to get exact U-100 syringe units.
Common: 5, 10, 15, 17, 20 mg/mL
Estimates weight loss based on SURMOUNT-1, 2, 3, and 4 clinical trial data. Individual results vary — this is a population-level projection.
Tirzepatide users need higher protein intake than average to preserve lean muscle mass during rapid weight loss. This calculator uses GLP-1-specific protein targets.
Tirzepatide has a half-life of approximately 5 days (120 hours). Steady state is reached after 4–5 half-lives of consistent weekly dosing (~4–5 weeks).
Always verify your vial's labeled concentration before injecting. Concentration may differ from your calculation if BAC water was already pre-mixed or if the vial is from a different batch. Confirm every dose with your prescribing provider or pharmacist.
Tirzepatide Dosing Chart — Complete Titration Schedule (2024/2025)
The FDA-approved tirzepatide titration schedule for both Mounjaro (type 2 diabetes) and Zepbound (weight management) follows a gradual dose-escalation pattern designed to minimise gastrointestinal side effects while building toward a therapeutic maintenance dose. The schedule below is based on the prescribing information approved by the FDA and supported by SURMOUNT phase III clinical trial data.
| Weeks | Dose | Injection Freq | Phase | Expected Weight Loss |
|---|---|---|---|---|
| 1–4 | 2.5 mg | Once weekly | Initiation | 1–3% of body weight |
| 5–8 | 5.0 mg | Once weekly | Escalation | 3–6% cumulative |
| 9–12 | 7.5 mg | Once weekly | Escalation | 5–10% cumulative |
| 13–16 | 10.0 mg | Once weekly | Escalation | 8–15% cumulative |
| 17–20 | 12.5 mg | Once weekly | Maintenance | 12–18% cumulative |
| 21+ | 15.0 mg | Once weekly | Max Maintenance | 15–22.5% cumulative |
Not everyone needs to reach 15mg. SURMOUNT trial data shows that many participants achieved clinically meaningful weight loss (≥10% of body weight) at doses of 5–10mg weekly. Your maintenance dose is determined by your prescribing clinician based on your individual response and tolerance — not by a fixed escalation to maximum dose. Some patients find their ideal dose and remain there long-term.
How to Reconstitute Tirzepatide: Step-by-Step Guide
Compounded tirzepatide comes as a lyophilised (freeze-dried) powder that must be mixed with bacteriostatic water (BAC water) before injection. This process — called reconstitution — transforms the powder into a stable injectable solution. Getting the reconstitution right is critical because errors in BAC water volume directly change the concentration, which changes your syringe units and actual dose delivered.
You need: tirzepatide vial (lyophilised powder), bacteriostatic water (BAC water — not sterile water), U-100 insulin syringes, alcohol swabs (70% isopropyl), clean surface, and gloves if available. Never use tap water, saline, or sterile water — BAC water contains 0.9% benzyl alcohol which prevents bacterial growth across multiple uses.
Use our reconstitution calculator above. The most common and practical approach is to choose a BAC water volume that gives you a clean, easy-to-draw concentration. For a 10mg vial: 2mL gives 5mg/mL (2.5mg = 50 units). For a 30mg vial: 3mL gives 10mg/mL (2.5mg = 25 units). Use the formula: Concentration = Vial mg ÷ BAC water mL.
Wash your hands thoroughly with soap for 20 seconds. Using a fresh alcohol swab, wipe the rubber stopper of both the tirzepatide vial and the BAC water vial. Allow 15 seconds to dry completely — alcohol must evaporate before puncturing or it can contaminate the solution.
Draw your calculated BAC water volume into the syringe. Insert the needle into the tirzepatide vial at an angle so the tip touches the inside glass wall — not the powder directly. Inject the BAC water slowly down the glass wall so it trickles onto the powder without force. This is the most commonly skipped step: direct injection onto the powder can degrade the peptide structure.
Gently swirl the vial in slow circular motions. Never shake vigorously — mechanical agitation breaks peptide bonds and degrades the active compound. The powder typically dissolves within 1–5 minutes, resulting in a completely clear, colourless solution. If cloudiness persists after 10 minutes of gentle swirling, or if you see particles, do not use the vial.
Write the reconstitution date and concentration (e.g., "10mg/mL — reconstituted 15 May") on the vial with a label or marker. Store immediately in the refrigerator at 36–46°F (2–8°C). Reconstituted tirzepatide is stable for 28–60 days refrigerated. Never freeze reconstituted tirzepatide — freeze-thaw cycles damage the peptide. Never leave reconstituted tirzepatide at room temperature for extended periods.
How to Calculate Tirzepatide Dose — The Formula Explained
The tirzepatide dosage calculation converts your prescribed dose in milligrams (mg) into syringe units on a U-100 insulin syringe. Understanding the math helps you catch errors and calculate confidently when using compounded tirzepatide from any vial size.
Reconstitution and Concentration Formula
mg to Units Conversion Formula (U-100 Syringe)
How Much BAC Water to Add — Working Backwards
Quick Reference: Common Tirzepatide Reconstitution Scenarios
| Vial Size | BAC Water | Concentration | 2.5mg = | 5mg = | 7.5mg = | 10mg = |
|---|---|---|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 50 units | 100 units | — | — |
| 10 mg | 2 mL | 5 mg/mL | 50 units | 100 units | — | — |
| 10 mg | 1 mL | 10 mg/mL | 25 units | 50 units | 75 units | 100 units |
| 15 mg | 1.5 mL | 10 mg/mL | 25 units | 50 units | 75 units | 100 units |
| 20 mg | 2 mL | 10 mg/mL | 25 units | 50 units | 75 units | 100 units |
| 30 mg | 3 mL | 10 mg/mL | 25 units | 50 units | 75 units | 100 units |
| 60 mg | 6 mL | 10 mg/mL | 25 units | 50 units | 75 units | 100 units |
What Is Tirzepatide and How Does It Work?
Tirzepatide (brand names Mounjaro® and Zepbound®, developed by Eli Lilly) is a dual GIP/GLP-1 receptor agonist approved by the FDA in May 2022 for type 2 diabetes (Mounjaro) and November 2023 for chronic weight management (Zepbound). It is a once-weekly subcutaneous injection that simultaneously activates two incretin hormone pathways — GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) — producing combined metabolic effects that exceed single-agonist drugs like semaglutide.
The SURMOUNT-1 phase III clinical trial — the largest obesity drug trial of its kind — showed that participants taking 15mg of tirzepatide weekly for 72 weeks lost an average of 22.5% of their body weight. A remarkable 91% of participants achieved at least 5% weight loss, and 57% achieved 20% or more — results that approach those seen only in bariatric surgery. Tirzepatide also improves insulin sensitivity, reduces HbA1c, lowers triglycerides, and can reduce blood pressure, making it a true cardiometabolic compound.
Tirzepatide is unique in targeting both GLP-1 and GIP receptors simultaneously. GLP-1 activation slows gastric emptying, reduces appetite, and improves insulin secretion. GIP activation enhances insulin release in a glucose-dependent manner and may improve fat cell metabolism. The combination produces greater weight loss than either mechanism alone.
Head-to-head SURMOUNT-5 trial data (2024) showed tirzepatide produced 20.2% weight loss vs 13.7% with semaglutide 2.4mg — a 47% greater relative reduction. Tirzepatide also reaches a higher maximum dose and has superior effects on HbA1c, triglycerides, and waist circumference in most comparative analyses.
Emerging evidence and off-label clinical use suggests tirzepatide may be particularly beneficial for women with PCOS (polycystic ovary syndrome), as insulin resistance is a central driver of PCOS pathophysiology. Weight loss of ≥10% can restore ovulatory cycles in many PCOS patients, and tirzepatide's insulin-sensitising effects may add benefit beyond weight loss alone.
Rapid weight loss on tirzepatide can include significant lean muscle mass loss — studies show 30–40% of weight lost may be lean tissue rather than fat. This is why protein intake recommendations are higher for GLP-1 users (1.2–2.0g/kg body weight) combined with resistance training 2–3 times per week. Our protein calculator above accounts for this.
Mounjaro vs Zepbound vs Compounded Tirzepatide — What's the Difference?
Many users searching for a tirzepatide calculator, reconstitution guide, or Mounjaro dosage calculator are working with compounded tirzepatide rather than brand-name products. It is important to understand the key differences — particularly around reconstitution, which only applies to compounded powder vials.
| Feature | Mounjaro® (Eli Lilly) | Zepbound® (Eli Lilly) | Compounded Tirzepatide |
|---|---|---|---|
| FDA Approval | ✓ Approved (T2D) | ✓ Approved (Obesity) | Not FDA approved |
| Form | Pre-filled pen | Pre-filled pen | Lyophilised powder vial |
| Reconstitution Needed | No | No | Yes (BAC water) |
| Dose Flexibility | Fixed doses only | Fixed doses only | Fully customizable |
| Typical Monthly Cost | ~$1,000–$1,200 | ~$1,000–$1,200 | $200–$500 |
| Active Molecule | Tirzepatide | Tirzepatide | Tirzepatide |
| Quality Assurance | FDA-supervised | FDA-supervised | Varies by compounder |
| Purity Verification | Standardised | Standardised | Requires COA review |
| Regulatory Status (2025) | Fully approved | Fully approved | 503A/503B oversight |
Important 2025 regulatory note: The FDA declared the tirzepatide shortage over in 2024, which placed restrictions on 503A compounding pharmacies. Compounded tirzepatide may still be available through 503B outsourcing facilities or under specific medical necessity criteria, but the legal landscape is evolving. Always source compounded tirzepatide from a licensed 503A/503B pharmacy with a valid Certificate of Analysis (COA) from third-party HPLC testing.