PrivacyEverything stays on your phone. No account, no tracking.
Your data
This clears your pen prices, savings log, weights and settings on this phone. It can't be undone unless you have a backup.
Tarbell version 1.0
Milestone
Currency
Pick the currency your pharmacy charges in. Your saved prices keep their numbers.
How Tarbell works
Tarbell is made for 4 dose tirzepatide pens, which are commonly described as taking 60 clicks to dial one full labelled dose. The ring shows those 60 clicks. Each click is the pen strength divided by 60, so on a 10mg pen, 5mg is 30 clicks.
Use the slider for quarter milligram steps, tap Custom to type any dose like 3.33mg, or drag the ring itself to pick a number of clicks and see the dose it gives. Tarbell rounds to the nearest whole click and tells you exactly what you'll get.
Doses per pen counts only the four standard doses (240 clicks). Any liquid left after that varies between pens, so Tarbell ignores it.
Costs are worked out from each pen's price per mg. If you're on a bigger pen than you need, your saving is against buying the smallest pen that covers your dose, so 4mg from a 15mg pen is compared with 5mg pens. If you're already on that smallest pen, the saving is against taking its full labelled dose, because each pen goes further. Tap Pens & prices to see your dose on every pen and which is best value. Tap the savings badge to see monthly and yearly figures, and set how often you inject.
By default Tarbell assumes you use leftover clicks at the end of a pen and top up from your next one, so nothing is wasted. If you bin leftovers, switch that off in Settings and costs count whole doses only. Splitting a dose across two pens means two injections and relies on the leftover being accurate, so ask your pharmacist first.
This is not medical advice. Click counting is not how pen makers intend their pens to be used. Check any dose change with your prescriber or pharmacist before you inject.
Tarbell pen click calculator
Support Tarbell
Tarbell is built and run by one person in their spare time. If it has helped you or saved you a bit of money, a coffee helps cover the running costs and keeps it improving.
No pressure at all. Thanks for using it either way.
Type in what your pharmacy charges for each pen. Tarbell then shows what your dose costs on each one and picks the best value.
Price per pen
Saved on this phone
Your savings
£0.00
£0saved a month
£0saved a year
£0saved per pen
Cost per dose
You pay£0.00
Full dose£0.00
Your saving
Your pens
Per pen
A pen lasts
Leftover per pen
Pens a year
How often you inject
DailyMonthly
How savings tracking works
Log with one tap. On the Savings tab, tap Log today's dose. Tarbell uses the pen and dose from your Clicks screen and the prices in Pens & prices.
Doses repeat on your schedule. A logged dose carries on every week (or whatever gap you choose) until you log a different one. Tap any day on the calendar to skip it or change it.
Older doses. Tap a past day and save the dose. If something was different back then, tap Change details to set the dose, the pen, or the price you paid at the time.
Took it late? Log it on the day you actually took it. If that's less than halfway to your next dose, Tarbell moves that week's dose to the new day instead of counting it twice. Later than that, it counts as your next dose taken early.
The normal way uses the same rules as the savings badge. If your pen is bigger than you need, a dose is compared with buying the smallest pen that covers it. If you're already on that pen, it's compared with taking the pen's full labelled dose.
Pens' worth saved is your total saving divided by the price of the pen you're using now.
Your log stays on this phone only. Use Back up or restore in Settings so you don't lose it.
Add Tarbell to your home screen
It opens full screen like a normal app, and works even without signal.
1Tap the Share button at the bottom of Safari
2Scroll down and tap Add to Home Screen
3Tap Add in the top corner
1Open your browser menu
2Tap Install app or Add to Home screen
3Confirm, and Tarbell appears with your other apps
Your weight
Drag along the chart to see each weigh in. The dashed line is your trend, which smooths out the day to day ups and downs.
How it adds up
Your weights
Tap one to change or delete it.
How levels are worked out
Tarbell uses the doses on your Savings calendar and a standard model for injected medicines. Each dose is absorbed over roughly the first day, peaks, then clears with a half life of about 5 days, so about half is gone after 5 days and a quarter is left after 10.
Doses overlap, so levels build over the first few weeks and then settle into a steady wave. The faded part of the line continues your current schedule four weeks ahead.
Next dose counts down to your next scheduled dose. Tap it to log or change today's dose.
Compare another dose shows how a different dose or gap between doses would look over the same dates.
Figures assume about 80% of each dose is absorbed. These are averages: real levels vary from person to person, so treat the chart as an illustration, not a measurement. Talk to your prescriber before changing how you dose.
Back up or restore
Your data lives only on this phone. Copy this backup code and keep it somewhere safe, like your notes app or an email to yourself.
Restore
Paste a backup code to bring your data back. This replaces everything on this phone.