The Mounjaro tracker app that keeps your log on your phone

What a Mounjaro tracker actually needs to record

Most people start by logging a date. Within a month or two that stops being enough, because the questions get more specific: was the nausea worse on 7.5 mg or is it the site, how many days of the pen are left, why does the appetite come back on day five, and did the last increase actually move the weight or was that a plateau ending on its own.

Answering any of those needs more than a date. A Mounjaro tracker worth using records, for every shot:

• Date and time, not just the date. The level curve between a Monday morning shot and a Monday night shot is twelve hours apart, and that is exactly the window where people notice the difference.
• Strength in milligrams, from 2.5 mg through to 15 mg, because tirzepatide is dispensed as six separate products rather than one dialled pen.
• Which pen it came out of – a KwikPen or a single-use pen. They behave differently and the reorder maths is different.
• Injection site, so the rotation is real rather than remembered.
• Pain, on a scale, because that is the only way to find out which sites are genuinely better for you rather than which one you have a feeling about.
• How you felt afterwards, and which side effects turned up on which day.
• Weight, on whatever cadence you actually weigh.

Penwise records all of that in one screen, and remembers your medication and dose so a repeat shot is a few taps. If your phone or watch has a resting heart rate for that day, it attaches it to the shot on its own.

Knowing where you are between shots, not just when you last injected

This is the difference between a log and a tracker. Tirzepatide has an elimination half-life of roughly five days, and a single dose peaks around a day after you inject it. Dose weekly and the curve never returns to zero: each shot lands on top of what is left of the last one, and it takes about four to five weeks of a stable dose before the peaks and troughs settle into the same shape every week.

That shape explains most of what people report. The heavy, sleepy, appetite-flattened days cluster near the peak. The week where the food noise creeps back tends to be the tail of the cycle, or the week after a missed dose, or the four weeks after an increase when the average level is still climbing.

Penwise+ draws that curve from the doses you logged, using published absorption and elimination rates for tirzepatide. It is a model, not a blood test – it does not know your body – but the timing and the shape are the useful part, and both come out of the arithmetic rather than out of guesswork. There is more on how it is calculated in how long Mounjaro stays in your system.

It knows the KwikPen, including the one that changed

Mounjaro is sold as two devices, and the difference matters to anyone counting supply.

Figures from the manufacturer leaflet. Click counts are a community reference, not manufacturer guidance – see the pen click chart.

The KwikPen also has a generation problem that catches people out. The original device finishes with a measurable amount of liquid left in it, which is where the “extra dose at the end” conversation comes from. Lilly began shipping a redesigned KwikPen in April 2026 that finishes essentially empty, so the leftover is not there any more. Both are in circulation, the box looks the same, and Penwise asks which one you have rather than assuming.

A tracker that does not know any of this can tell you a pen is “in use”. Penwise counts down the thirty days, tells you how many days of supply are left at your current dose, and warns you when a stretched dose would outlast the discard window before it outlasts the liquid. That last one is the failure most people only find out about the hard way.

Side effects, timed against the dose rather than the calendar

Nausea on a Thursday means nothing on its own. Nausea on day two after every shot, easing by day four, and returning the week you moved from 7.5 mg to 10 mg is a pattern, and it is one you can plan around.

Penwise tracks twenty named side effects on a 0 to 5 scale, from nausea and constipation through to hair loss and injection anxiety, plus nine things on a sliding scale: appetite, fullness, food noise, sweet, salty and fatty cravings, energy, mood and sleep. Then it looks for the timing. If a symptom reliably lands on the same day after your shots, the Insights tab says so – and if it does not have enough of your history to be sure, it says nothing at all rather than inventing a pattern from three data points.

The full picture of when things tend to arrive is in the GLP-1 side effect timeline.

Injection sites that rotate for real

Tirzepatide goes into the abdomen, thigh or upper arm, and rotating matters over months rather than weeks. The problem is that nobody remembers where the last four shots went.

Penwise puts the sites on a body map, suggests the one you have used least recently, and stores the pain you recorded against each. After a couple of months that becomes a real answer to “which site is least unpleasant for me” – which is usually not the site people assume. There is more detail in GLP-1 injection sites.

The report your prescriber can actually read

Appointments about GLP-1 treatment tend to run on memory: roughly how much weight, roughly what side effects, roughly whether you have been on time. A tracker fixes that if it can hand over something legible.

Penwise+ generates a PDF with your dose history, weight trend, adherence and the side effects you recorded, dated and in order. You can hand it over at the appointment or send it ahead. There is a clinical-standard export too, and CSV and JSON export is free forever – your own history is never behind a paywall.

Why the log stays on your phone

A tirzepatide history is a record of a prescription, a body weight and a set of symptoms. It is exactly the sort of thing people are careful about, and most trackers in this category ask you to make an account and then hold it for you.

Penwise does not. There is no account, no email address, no sign-in, and no Penwise server that health data reaches. Everything you log lives in the app on your device. There are no ad-network SDKs and no third-party analytics on any of it. The only copy that ever leaves the phone is a backup you export yourself, encrypted on the device with a passphrase we do not hold.

That is an architectural claim rather than a policy one, which is the point: a policy can be changed quietly, and this cannot. If it matters to you, why a GLP-1 tracker should not have a server goes into it properly.

What it costs

The core Mounjaro tracker is free forever: logging shots and oral doses, weight and trend, site rotation on a body map, full history and calendar, cravings and appetite, dose reminders, and full CSV and JSON export.

Penwise+ adds the estimated level curve, the Insights tab, nutrition and protein tracking, Apple Health and Health Connect sync, doctor-ready PDF reports, Shotsy import, the share card studio and the colour themes. It is 2,49 € a month, 19,99 € a year, or 59,99 € once and never again, and every install starts with a fourteen-day trial of everything that needs no card and no account. See the full pricing.

Common questions

Sources

Every factual claim on this page traces to the product information a regulator publishes, or to a published trial. Links open on the site of whoever issued the document.

1. Mounjaro: EPAR product information European Medicines Agency
2. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1) New England Journal of Medicine, 2022
3. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5) New England Journal of Medicine, 2025
4. Tirzepatide for managing overweight and obesity (TA1026) National Institute for Health and Care Excellence

Penwise is a tracking and education tool, not a medical device. Nothing on this page is medical advice, a diagnosis or a recommendation to start, stop or change a dose. Dosing decisions belong to you and your clinician. Ozempic, Wegovy, Rybelsus, Saxenda and Victoza are trademarks of Novo Nordisk; Mounjaro, Zepbound and Trulicity are trademarks of Eli Lilly. Penwise is not affiliated with, endorsed by or connected to either company.