Tirzepatide Tracker: Weekly Doses, Late Shots and the Curve in Between

What is tirzepatide, and how do Mounjaro and Zepbound differ?

Tirzepatide is a once-weekly injection from Eli Lilly that activates two receptors, the glucose-dependent insulinotropic polypeptide receptor and the glucagon-like peptide-1 receptor.^[3] Mounjaro and Zepbound contain the same molecule under different labels. The Mounjaro label covers glycemic control in adults and in children aged 10 and over with type 2 diabetes, and a lower risk of cardiovascular events in some adults.^[1] The Zepbound label covers reducing excess body weight in adults with obesity or overweight and weight-related conditions, and treating moderate to severe obstructive sleep apnea in adults with obesity.^[2] For a tracker this means one drug with two entry names. PepTrac uses the same half-life data for both, so name the entry after the product on your prescription and enter the dose you actually injected. Your prescriber chooses the product and the dose.

What does the label say about a missed tirzepatide dose?

Both labels use the same window. The Mounjaro label says to give a missed dose as soon as possible within 4 days, which it states as 96 hours, after the missed dose.^[1] The Zepbound label gives the same window.^[2] If more than 4 days have passed, the labels point you back to your regular day, and your prescriber or pharmacist is the right person to confirm what applies to you. The hard part is counting. After a travel week or a change of routine, many people cannot say whether it has been 3 days or 5 since the shot was due. A tracker settles that with one number. PepTrac lists your recent doses with how long ago each was, next to the next-dose countdown, so you compare your own count with the label text. It does not tell you whether to take a late dose.

What does a skipped week do to the estimated level?

PepTrac's model only counts doses you log, so a skipped week shows up as a lower curve. Take four weekly doses of 2.5 mg, the label starting dose, as an arithmetic input. The level just before the fifth dose reads 1.79, with a range of 1.26 to 2.31. If the fourth dose is skipped, day 28 reads 0.66 with a range of 0.37 to 0.98. The model uses a half-life of 120 hours, close to the 5 days on the Mounjaro label.^[1] These are relative units scaled to each dose, not blood concentrations, and the range comes from changing the half-life and peak time by 20 percent each. The chart is a visual aid for a conversation with your prescriber. It cannot say what a skipped dose means for you, and it is not a lab result.

How do tirzepatide doses step up on the label?

Both labels begin at 2.5 mg injected under the skin once weekly. The Mounjaro label then raises the dose in 2.5 mg increments after at least 4 weeks on the current dose, to a maximum of 15 mg in adults.^[1] The Zepbound label starts at 2.5 mg for 4 weeks, raises it in 2.5 mg steps after at least 4 weeks, and lists maintenance doses of 5, 10 or 15 mg for weight reduction.^[2] The definitions below give each term in label language. Notice that the labels set a minimum time per step, not a fixed calendar, so your own schedule may be slower than the minimum. A tracker should store the schedule you were given. PepTrac keeps it as steps of dose plus duration and holds the last step. It never picks the next step for you, because that call belongs to your prescriber.

Starting dose

2.5 mg once weekly on both labels.^[1][2]

Step size

2.5 mg increments.^[1][2]

Minimum time per step

At least 4 weeks on the current dose.^[1][2]

Maximum dose

15 mg once weekly in adults.^[1][2]

Missed-dose window

Within 4 days (96 hours) after the missed dose.^[1][2]

How long does tirzepatide stay in your body?

The Mounjaro label gives an elimination half-life of approximately 5 days, a time to maximum plasma concentration of 8 to 72 hours, and steady-state concentrations after 4 weeks of once-weekly dosing.^[1] The Zepbound label gives a half-life of approximately 5 to 6 days.^[2] A drug with a 5-day half-life keeps about half of a dose after 5 days, a quarter after 10 days, and so on, which is why one missed week lowers the level without erasing it. These numbers describe the average in trial participants, so any one person will differ. PepTrac turns them into a curve using 120 hours as the half-life and 24 hours as the time to peak, then draws a range around it. For the decay arithmetic on its own, see tirzepatide half-life. Whether a level means anything for your health is a question for your clinician.

Can you track Zepbound vials as well as pens?

Yes. The Zepbound label lists single-dose pens and vials, each a 0.5 mL solution, and a multi-dose vial and KwikPen that hold 4 doses, in strengths from 2.5 mg to 15 mg per injection.^[2] A pen delivers the dose in milligrams, so you log the number on the pen. A vial dose is drawn on a syringe, so the log needs the vial size, the volume and the syringe units. The FDA reports more than 730 adverse event reports for compounded tirzepatide as of May 31, 2026, with some cases involving dosing beyond the approved label amounts, which is a reason to keep exact records and check the units twice.^[5] The tirzepatide dose calculator converts a dose you enter into units. PepTrac does the same conversion inside each compound and keeps the vial fill level. It converts the values you enter, so confirm each result with your label and pharmacist.

How did tirzepatide perform in clinical trials?

Two large trials give the standard figures. SURMOUNT-1 enrolled 2,539 adults with obesity or overweight and no diabetes and compared tirzepatide 5, 10 and 15 mg with placebo for 72 weeks. The mean change in weight was 15.0, 19.5 and 20.9 percent on tirzepatide against 3.1 percent on placebo, and gastrointestinal events were the most common, mostly during dose escalation.^[3] SURPASS-2 enrolled 1,879 adults with type 2 diabetes and compared tirzepatide with semaglutide 1 mg for 40 weeks. HbA1c fell by 2.01, 2.24 and 2.30 percentage points on tirzepatide against 1.86 on semaglutide, and body weight fell more on tirzepatide.^[4] Both were phase 3 trials, and Eli Lilly funded both. Trial averages describe groups and are not a prediction for any one person. Logging doses and weight over many months is how you build your own picture.