GLP-1 pen leftover calculator

What is actually left in your pen?

Two questions the label already answers and nobody reads back to you: at the dose you are dialing, how many injections is this pen, and which week does the next one have to be in your hand? For the multi-dose pens — Ozempic and Saxenda — the count below is built from the fill volume on the FDA label. For Wegovy, Zepbound and Mounjaro the answer is always one, and the reason is worth knowing before you go looking for a second.

Start here: which kind of pen do you have?

Single-dose pens

Wegovy · Zepbound · Mounjaro

One pen is one weekly injection, and then it is disposed of. Leftover is not a category here: the device dispenses a single dose by design and does not reset. Whatever stays inside is meant to stay inside, and a syringe will not change that.

Multi-dose pens

Ozempic · Saxenda

One cartridge, several injections, each one dialed by you. The calculator below counts what remains and names the week your refill has to arrive by.

Multi-dose pen calculator

Use this for Ozempic and Saxenda. (Wegovy, Zepbound, and Mounjaro pens are single-dose — see the card above.)

PenDose dialed per injectionDoses already taken from this penDays since you started this pen (optional)

Your pen, by the numbers

Total doses in this pen

at 1 mg per week

Doses remaining

0 taken

Volume remaining

3 mL

0.75 mL per dose

Days of supply remaining

28 days

weekly dosing

On the schedule you entered, the pen empties around Nov 1, 2026. Put the refill request in one to two weeks before that, which is what keeps the weeks unbroken.

Educational tool only — not medical advice. All fill volumes and dose counts are taken from the FDA prescribing information for each pen. Never attempt to extract drug from a pen with a syringe; sterility and dose accuracy cannot be guaranteed outside the pen’s metered mechanism.

Every multi-dose pen, by the label

Taken from each pen’s FDA prescribing information. The dose count is fill / dose volume rounded down, and it is a ceiling rather than an estimate: the stop built into the pen will not let it dispense past the labeled number.

Pen	Fill	Dose	Doses per pen	Schedule
Ozempic 0.25/0.5 mg starter pen 2 mg / 3 mL	3 mL	0.25 mg	4	Weekly
Ozempic 0.25/0.5 mg starter pen 2 mg / 3 mL	3 mL	0.5 mg	4	Weekly
Ozempic 1 mg pen 4 mg / 3 mL	3 mL	1 mg	4	Weekly
Ozempic 2 mg pen 8 mg / 3 mL	3 mL	2 mg	4	Weekly
Saxenda 18 mg/3 mL pen 18 mg / 3 mL	3 mL	0.6 mg (week 1)	30	Daily
		1.2 mg (week 2)	15	Daily
		1.8 mg (week 3)	10	Daily
		2.4 mg (week 4)	7	Daily
		3.0 mg (maintenance)	6	Daily

Why the extra liquid is not an extra dose

Brand GLP-1 pens are filled a little above their labeled total. That margin is there so the last rated dose still comes out whole after priming has taken its share and after the small volume that never leaves the cartridge deadspace. It is visible enough that people ask the obvious question about it.

Two things in the labels rule it out, and either would settle it alone:

The dial stops. Ozempic and Saxenda carry a physical stop that engages once the cartridge has given up the volume it was rated for. Whatever is still in there, the selector will not travel far enough to set a full dose against it.
Nothing past the label was measured. The margin is a tolerance of a few percent, not a reserve. It is nowhere near a whole injection, and it varies from pen to pen, so anything recovered from it is an unknown quantity — plausibly well under the milligrams you believe you just took, and possibly over.

What to do with what is left

Dispose of the pen the way its label tells you to. Do not draw the residue off with an insulin syringe: opening a cartridge to the air ends any sterility guarantee it came with, and no manufacturer has ever measured the accuracy of a hand-drawn dose out of a brand pen. If the real problem is the gap between refills, say that to your prescriber. An early refill or a bridge script is a routine request at most telehealth clinics.

Compounded vials are different

Everything above is about brand pens. A compounded vial of semaglutide or tirzepatide, reconstituted with bacteriostatic water and sold for multiple uses, is a different object: no dial, no stop, and every dose measured out by hand with an insulin syringe. There the question stops being how many are left and becomes one of units. See our compounded GLP-1 reconstitution guide and the GLP-1 unit converter for the math.

References

1.Novo Nordisk Inc. OZEMPIC (semaglutide) injection — US Prescribing Information, Section 3 Dosage Forms and Strengths and Section 16 How Supplied (multi-dose pen fill volumes and labeled dose counts). FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/209637s035,209637s037lbl.pdf
2.Novo Nordisk Inc. WEGOVY (semaglutide) injection — US Prescribing Information, Section 16 How Supplied (single-dose prefilled pen). FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215256s026lbl.pdf
3.Novo Nordisk Inc. SAXENDA (liraglutide) injection — US Prescribing Information, Section 3 Dosage Forms and Strengths (18 mg/3 mL multi-dose pen). FDA Approved Labeling. 2024. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/206321s022lbl.pdf
4.Eli Lilly and Company. MOUNJARO (tirzepatide) injection — US Prescribing Information, Section 16 How Supplied (single-dose prefilled pen). FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215866s039lbl.pdf
5.Eli Lilly and Company. ZEPBOUND (tirzepatide) injection — US Prescribing Information, Section 16 How Supplied (single-dose prefilled pen and single-dose vial). FDA Approved Labeling. 2025. https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/217806s002lbl.pdf

Related research and tools

GLP-1 storage and shelf life — what the label allows in the fridge, and the 56 days it allows at room temperature
Wegovy pen vs compounded vial — a single-dose pen set against a multi-use vial, start to finish
Where and how a GLP-1 is injected — the technique itself, for a pen and for a syringe
GLP-1 unit converter — milligrams to insulin-syringe units, for a compounded vial
GLP-1 washout calculator — what the drug is still doing after your final injection

Frequently asked questions

How many injections does one Ozempic pen hold?

Section 3 of the Ozempic label answers this by strength. The starter pen carries 3 mL holding 2 mg of semaglutide, rated for four weekly injections, taken either at 0.25 mg or at 0.5 mg. Step up and the 1 mg pen holds 4 mg in 3 mL, again four injections; the 2 mg pen holds 8 mg in 3 mL, again four. Whichever strength is in your hand, the label rates it at four weeks.

Is there a spare injection hiding in a Wegovy pen?

No. A Wegovy pen fires once: one weekly injection, then the sharps container. There is more liquid in the cartridge than the labeled dose, but that is manufacturing tolerance rather than a spare, and the mechanism will not dispense it. Going after it with a syringe is not a workaround.

My Saxenda pen still has liquid in it. Now what?

Throw it away 30 days after the first injection, whether or not liquid is still visible. That window is what the preservative system was tested to hold, and a part-full cartridge does not extend it. Pulling the residue into a syringe gives up both sterility and the metered dose the pen exists to deliver. Order the refill before the pen runs down, not after.

If the refill is late, can I take a part-dose?

No. On Ozempic and Saxenda the dial reaches a stop once the cartridge has given up its rated number of doses, so a full injection is no longer mechanically on offer. Nothing smaller has been validated for accuracy on any GLP-1 pen either. A refill that has not arrived belongs with your prescriber, not with a syringe or a borrowed second pen.

How long does an Ozempic pen last?

Four weeks, at whichever dose it is labeled for — that holds for the 2 mg, 1 mg, 0.5 mg and 0.25 mg strengths alike. One case runs longer: still at the 0.25 mg starting dose, the starter pen covers eight weeks rather than four. Separately, the label allows 56 days at room temperature after the first use.

I dialed past the dose I meant. What now?

Both pens dial backwards without wasting anything — turn the selector back down until the window shows the dose you meant. If the injection has already happened, call your prescriber or poison control. Do not decide on your own to miss the following week: what should happen next depends on the drug, the amount and how you feel, and that is a clinical judgment.

Important disclaimer

Educational only, and not medical advice. Every fill volume and dose count here is read off the FDA prescribing information for that pen and from nowhere else. If you are unsure whether a dose remains, ask the clinician who wrote the prescription rather than working it out yourself, and do not take drug out of any GLP-1 pen with a syringe — single-dose or multi-dose, the answer is the same.

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