Free GLP-1 calculators that give you a number, not a lecture.

Pen or vial? Start here

Almost every wasted visit to a dose calculator starts the same way: someone holding a pen lands on a tool built for a syringe. What you are holding decides which arithmetic applies to you — and whether any applies at all.

Preset really does mean preset. The Ozempic 2 mg/3 mL pen delivers four doses of 0.25 mg followed by two doses of 0.5 mg (or four doses of 0.5 mg), the 4 mg/3 mL pen delivers four doses of 1 mg, and the 8 mg/3 mL pen delivers four doses of 2 mg, per the Ozempic US prescribing information. No unit conversion applies to any of them.

Which calculator do you actually need?

Most people arrive here with one of five questions, phrased more or less like this. Each maps to the tool that answers it, so you can skip the grid.

What each calculator asks you for

Nothing here needs an account, and nothing is stored. Before you open one, this is exactly what it wants from you, what it hands back, and what the answer rests on.

Two kinds of tool on this page

It's worth knowing which sort you're using, because the failure modes differ. Unit-conversion calculators — the mg-to-units, vial, click and split tools — are arithmetic on numbers you supply, and are only ever as right as the concentration you type in.

Planning and nutrition estimators — the projector, plotter, protein, water, fibre and ideal-weight tools — model a population average, not you. They are useful for setting expectations and spotting when something has drifted, and useless as a target to chase. A trial average hides enormous individual variation in both directions.

How these calculators are built

Dose ladders, missed-dose windows, half-lives and steady-state timings come from the current prescribing information for each drug, not from secondary summaries of it. Weight-loss projections use published means from the pivotal trials. Where a figure varies between the US label and the UK SmPC — and several do — the individual tool page says which one it is quoting.

Every tool page carries its own sources list linking the exact document behind its numbers, so you can check the arithmetic against the label rather than trusting us. The primary references across the set are:

• Zepbound (tirzepatide) US prescribing information and Mounjaro (tirzepatide), via DailyMed
• Ozempic (semaglutide) and Wegovy (semaglutide) US prescribing information
• Mounjaro UK Summary of Product Characteristics — in the UK, tirzepatide is licensed as Mounjaro for both diabetes and weight management; there is no UK Zepbound
• The STEP 1, SURMOUNT-1 and SURMOUNT-5 trials, for weight-loss magnitudes

The waiting built into the titration planner comes from the same place: tirzepatide reaches steady-state plasma concentrations after four weeks of once-weekly dosing, with an elimination half-life of roughly five to six days, which is why the label spaces escalation steps four weeks apart.

None of this is medical advice, and no calculator here can tell you what your dose should be. They exist to make the arithmetic visible so that the conversation with your prescriber starts from the same numbers.

Read the guide behind the number

A calculator answers a question in one number. If you want the reasoning underneath it, these go with the tools — and there is more in the GLP-1 FAQ and guides.

• The 2026 GLP-1 dose conversion chart for Wegovy, Ozempic, Mounjaro and Zepbound — the ladders the titration planner is drawing from.
• How many mL and how many doses are in a Zepbound vial — the question behind the vial calculator.
• How to actually hit your GLP-1 protein floor when you can't eat — the eating problem the protein number does not solve on its own.
• The retatrutide reconstitution maths, explained honestly — including what is not known about it.
• The Zepbound titration ladder, step by step — why each step lasts as long as it does.

Common questions about GLP-1 calculators

Is there a free GLP-1 calculator?

Yes. This page hosts 19 free GLP-1 calculators with no signup and no email: mg-to-unit conversions, vial transitions, pen clicks, titration dates, dose plotting, protein and fibre floors, hydration, ideal weight and cost per pound. Each one names the document its numbers come from.

Which GLP-1 calculator do I need for a vial?

It depends on the vial. With a manufacturer single-dose vial the whole vial is one dose, so you are confirming units against the strength on the label. With a compounded multi-dose vial you are dividing your dose by the concentration to get units, and re-doing that division every time the strength changes.

Do GLP-1 pens need a dose calculator?

No. Branded Ozempic, Wegovy, Mounjaro and Zepbound pens deliver preset doses, so there is nothing to convert, and no manufacturer publishes a click count for them — Lilly says the Mounjaro KwikPen Instructions for Use give no method for dialling less than the full fixed dose, so it is not recommended. Pen users need timing tools instead: the missed-dose window for their brand, the titration ladder, and how the drug level builds between shots. (Ozempic US prescribing information)

What does 5 mg/0.5 mL mean on a vial?

It means the vial holds 5 mg of drug in half a millilitre, which is a concentration of 10 mg per mL — not 5 mg per mL. Vial labels state an amount and a volume, not a concentration. Divide before you draw, or every unit is double what you intended. (Zepbound US prescribing information)

Last updated 5 August 2026. Dose ladders, missed-dose windows and half-lives are re-checked against the current prescribing information, and each tool page names the document it is quoting.