Tirzepatide Dose Calculator

What is Tirzepatide?

Tirzepatide is a once-weekly injectable medication that activates two gut hormone receptors, GIP and GLP-1. It is sold as Mounjaro for type 2 diabetes and as Zepbound for chronic weight management. Both contain the identical drug, are injected once a week, and follow the same 2.5 mg to 15 mg dose schedule.

That dual action is what sets tirzepatide apart from semaglutide, which acts on GLP-1 alone. In the SURMOUNT-1 trial, adults without diabetes taking 15 mg lost an average of about 21 percent of their body weight over 72 weeks, the largest average reduction seen with any approved anti-obesity medication to date.

Because the drug acts strongly on the digestive system, treatment always starts at a low dose and steps up gradually, a process called titration. This calculator maps exactly where you are in that process.

How Tirzepatide Works

Tirzepatide mimics two hormones your gut releases after eating, GIP and GLP-1. Together they slow stomach emptying, increase insulin release when blood sugar is high, suppress glucagon, and act on appetite centres in the brain. The result is that you feel full sooner, stay full longer, and feel hungry less often.

The practical consequence is that the calorie deficit happens on its own. You are not fighting hunger with willpower, which is why the medication works where dieting alone often fails. It also explains the side effects: the same slowed digestion that keeps you full is what causes nausea and constipation.

It also explains why what you eat during treatment matters so much. When total intake falls without effort, protein is usually the first thing to drop, and that is precisely what puts your muscle at risk.

FDA Weekly Dose Schedule

Tirzepatide starts at 2.5 mg once weekly for 4 weeks, then increases to 5 mg. After that, the dose can rise in 2.5 mg steps, with at least 4 weeks at each step, up to a maximum of 15 mg weekly. Mounjaro and Zepbound share this schedule exactly.

The 2.5 mg starting dose is an initiation dose. It is not intended to control blood sugar or produce weight loss, so judging whether the medication is working during your first month is premature by design.

Dose Escalation Timeline

Each tirzepatide dose is held for at least 4 weeks before stepping up 2.5 mg. Four weeks matters for two reasons: tirzepatide has a half-life of about 5 days, so blood levels take roughly 4 weeks to plateau at any new dose, and gradual increases give your gut time to adapt, which sharply reduces nausea and vomiting.

Escalation is not automatic. Many people stay at 5 mg or 10 mg for months because it is working, and prescribers routinely delay a step-up, or drop back a level, when side effects are hard to tolerate. Both are normal, FDA-anticipated adjustments rather than setbacks.

The maximum is 15 mg weekly. There is no approved dose above it, and reaching the top of the ladder is not a goal in itself: the right dose is the lowest one that gives you the result you need.

Mounjaro vs Zepbound: What Is the Difference?

Mounjaro and Zepbound are the same drug, tirzepatide, made by the same manufacturer, with the same 2.5 mg to 15 mg weekly schedule. The difference is the approved indication: Mounjaro is approved for type 2 diabetes, Zepbound for chronic weight management and obstructive sleep apnoea in adults with obesity. That distinction mostly affects insurance coverage.

Expected Weight Loss on Tirzepatide

In the 72-week SURMOUNT-1 trial, adults with obesity and without diabetes lost an average of 15 percent of body weight on 5 mg, 19.5 percent on 10 mg, and 20.9 percent on 15 mg, compared with about 3 percent on placebo. Results in people with type 2 diabetes are typically somewhat lower.

These are averages over 72 weeks, not promises, and the curve is not linear. Loss is usually slow during the 2.5 mg initiation month, accelerates through escalation, then flattens as your body approaches a new set point. A plateau is the expected shape of the curve, not a sign of failure.

Tirzepatide Half-Life Explained

Tirzepatide has an elimination half-life of about 5 days, which is what makes once-weekly dosing possible. Each dose adds to what remains of the previous ones, so levels climb for roughly 4 weeks after starting or increasing a dose before settling into a stable weekly rhythm called steady state.

Two practical consequences follow. First, a new dose does not show its full effect immediately: give it about 4 weeks before judging it. Second, washout is slow. After your last injection, meaningful drug activity persists for weeks, which is why effects taper off gradually rather than stopping the day you stop.

It is also why a missed dose is not an emergency. If fewer than 4 days have passed you can usually take it and keep your schedule, and if the gap is longer your prescriber decides whether to skip it or restart lower.

What Estimated Drug Activity Means

Estimated drug activity is how close your blood level is to the plateau for your current dose. With a 5-day half-life, each weekly injection stacks on the remains of earlier ones, so levels rise for about 4 weeks after any dose change. A figure near 100 percent means your current dose is fully established.

It is a model, not a measurement. The number is calculated in your browser from published pharmacokinetics and the dose and week you entered, and it does not reflect a blood test. Its practical use is to tell you whether a dose has had a fair chance to show what it can do yet.

Protein Needs on Tirzepatide

Aim for roughly 1.2 to 1.6 grams of protein per kilogram of body weight per day during active weight loss, spread across every meal. Appetite suppression makes protein the easiest macro to under-eat, and low protein during rapid loss is what turns fat loss into muscle loss. Your snapshot above calculates your personal target.

Pair that protein with resistance training two or three times a week. Together they are the best-evidenced way to keep the weight you lose coming from fat. Protein first at every meal is the single most useful habit on this medication, because you will simply run out of appetite before you run out of plate.

Hydration on Tirzepatide

Aim for about 30 to 35 ml of fluid per kilogram of body weight daily, roughly 2 to 3 litres for most adults, and more during nausea or vomiting. Tirzepatide dulls thirst signals along with hunger, and GI side effects increase fluid loss, so dehydration creeps up quietly.

Consistent hydration measurably reduces two of the most common complaints on this drug: headaches and constipation. If you only change one habit during escalation weeks, make it this one.

Exercise on Tirzepatide

Resistance training two to three times a week is the highest-value exercise on tirzepatide, because it is the signal that tells your body to keep muscle while it sheds fat. Add about 150 minutes of moderate cardio weekly for cardiovascular health. Neither needs to be elaborate to work.

Schedule harder sessions away from the 24 to 48 hours after your injection if that window is when nausea and fatigue hit you. Consistency across the month matters far more than intensity in any single session.

Common Side Effects of Tirzepatide

The most common tirzepatide side effects are gastrointestinal: nausea, diarrhoea, constipation, vomiting and indigestion. They are usually mild, appear in the first weeks at any new dose, and fade as your body adapts. Gradual titration exists specifically to keep them manageable.

• Nausea: the most common effect, usually worst in the days after an injection or a dose increase
• Constipation or diarrhoea: often improved with fibre, fluid and daily movement
• Early satiety: feeling full very quickly, so eat smaller, protein-first meals
• Fatigue and headache: most common during escalation weeks and often linked to under-eating or dehydration
• Injection-site reactions: rotate between abdomen, thigh and upper arm
• Hair thinning: usually a response to rapid weight loss rather than the drug itself, and typically temporary

When to Contact Your Doctor

Most tirzepatide side effects are mild and self-limiting, but a few warrant prompt medical attention. Contact your prescriber or seek urgent care if you experience any of the following, and never adjust your dose on your own to manage them.

• Severe or persistent abdominal pain, especially pain that radiates to your back, which can signal pancreatitis
• Persistent vomiting, or any inability to keep fluids down
• Signs of dehydration such as dizziness, dark urine or a racing heart
• Symptoms of low blood sugar, particularly if you also take insulin or a sulfonylurea
• A lump or swelling in your neck, hoarseness, or trouble swallowing
• Severe allergic reaction: rash, swelling of the face or throat, or difficulty breathing, which is a medical emergency
• Vision changes if you have diabetic retinopathy