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How long will my vial last?
See how many doses and weeks a vial will last – and what each dose actually costs.
The short answer
Doses per vial is the total amount of drug divided by your dose. A 10 mL vial at 200 mg/mL holds 2,000 mg, so 100 mg twice a week is 20 doses and about 10 weeks. Cost per dose is the vial price divided by that dose count.
Two things bend the arithmetic in practice. Every draw leaves a little drug behind in the syringe and needle, so you get fewer usable doses than the division suggests. And an opened vial has an in-use limit that is independent of how much is left in it – if that limit lands before you finish, the remainder is discarded and your real cost per dose is higher than the number above.
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A vial runs out twice
Every vial has two end dates and the earlier one wins. The first is the one this calculator computes: you inject the last dose and the vial is empty. The second is the in-use limit – the point after opening at which the contents are no longer considered fit to inject, regardless of how much is sitting in the glass. Most cost-per-dose arithmetic online only models the first, which is why it flatters big vials.
| Container | Typical in-use limit | Where the number comes from |
|---|---|---|
| Multi-dose vial, preserved | 28 days from first puncture | The CDC's injection-safety convention for a punctured multi-dose vial, applied unless the manufacturer states otherwise. It is an infection-control rule about the preservative, not a statement that the drug has degraded. |
| Single-dose vial | The procedure it was opened for | Single-dose vials carry no preservative, so CDC guidance is one patient, one procedure, then discard. “Doses per vial” is not a meaningful question for these. |
| Semaglutide pen (Ozempic) | 56 days after first use | Product labelling. Wegovy pens are single-dose. Mounjaro comes both ways: the single-dose pen has no in-use limit. The multi-dose KwikPen holds four weekly doses. That one is discarded 30 days after first use. |
| Reconstituted peptide | Commonly about 28 days refrigerated | Bacteriostatic water's preservative convention. Actual peptide stability varies by compound and is the harder constraint – see the storage and shelf-life guide. |
| Reconstituted hCG | About 30 to 60 days refrigerated | Varies by product labelling. Check the leaflet that came with yours rather than a forum figure. |
These are the conventions applied in clinical settings. A commercial multi-dose vial you were dispensed may be labelled for use until its printed expiry date instead, which is why the in-use field above defaults to None. Use the number on your own label or the one your prescriber gave you, not the strictest one on this table. Educational information, not medical advice.
Why you get fewer doses than the arithmetic says
Divide 2,000 mg by 100 mg and you get 20. Draw twenty times and you will usually find the vial empty somewhere around the eighteenth. The gap is dead space: the volume that stays in the syringe hub and needle after the plunger bottoms out. It is drawn from the vial and it is not injected.
- Insulin syringe, needle permanently attached – roughly 1 to 5 µL. Negligible.
- Luer-lock syringe with a detachable needle – roughly 35 to 100 µL, around 70 µL being typical.
At 200 mg/mL, 70 µL is 14 mg. On a 100 mg dose that means each injection actually consumes about 0.57 mL rather than 0.50 mL, so a 10 mL vial yields about 17 doses instead of 20 – roughly 12% fewer. Working against it, manufacturers slightly overfill vials so the full labelled volume can be withdrawn, which recovers some of that. The practical rule: if you draw with a detachable needle, treat the calculated dose count as an upper bound, and if you want the arithmetic to hold, draw and inject with the same fixed-needle syringe.
Two smaller effects worth knowing. Syringe graduations quantise your dose – a U-100 insulin syringe marks 0.01 mL steps, which at 200 mg/mL is 2 mg per mark, so a “92.5 mg” dose is not a thing you can actually draw. And swapping to a fresh needle for the injection after drawing with a blunter one adds that needle's dead space to the loss.
Cost per dose is not cost per mg
Vial pricing is quoted per vial, compared per mg, and paid per dose. Those three diverge, and the divergence is exactly where an in-use limit does its damage.
Cost per mg rewards the biggest vial every time, because the price of glass, filling and shipping is spread over more drug. Cost per usable dose does not, because a vial you cannot finish inside its in-use window bills you for the part you throw away. Where a limit binds, the honest comparison is:
- Cost per dose = vial price ÷ doses per vial. What most calculators, including the one above, report first.
- Cost per usable dose = vial price ÷ the doses you can actually give before the limit. Always equal to or worse than the first number.
- Cost per week = cost per dose × injections per week. The figure to use when comparing protocols with different frequencies, since a daily protocol and a twice-weekly one at the same weekly total cost the same here.
This is why a smaller vial can be the cheaper choice despite a worse price per mg. If a 10 mL vial is discarded 60% full at day 28 and a 2 mL vial is finished, the 2 mL vial wins on the only number that matters.
Worked examples
Four common configurations, run through the same arithmetic the calculator uses. The last column assumes the in-use limit from the table above actually applies.
| Vial | Dose & frequency | Doses | Lasts | If the limit applies |
|---|---|---|---|---|
| Testosterone 10 mL @ 200 mg/mL 2,000 mg total | 100 mg, 2×/week | 20 | 10 weeks | A 28-day limit would cut it to 8 doses and discard 1,200 mg. Check your label – many dispensed multi-dose vials run to their printed expiry instead. |
| Testosterone 2 mL @ 200 mg/mL 400 mg total | 100 mg, 2×/week | 4 | 2 weeks | Finished well inside any limit. Worse per mg, no waste. |
| Semaglutide 5 mg vial | 0.25 mg, 1×/week | 20 | 20 weeks | A compounded vial is a preserved multi-dose vial, so the 28-day convention applies rather than the pen’s 56 days: 4 doses used, 4 mg discarded. This is the case where the small vial is plainly cheaper. |
| BPC-157 10 mg vial | 250 mcg, daily | 40 | 5.7 weeks | 40 days of dosing against a roughly 28-day reconstituted window. Reconstituting in two halves only helps if the second half stays sealed and sterile until it is used; opening a vial twice to split it is how the window gets shorter rather than longer. |
| hCG 5,000 IU vial | 500 IU, 2×/week | 10 | 5 weeks | 35 days sits inside a 60-day window and outside a 30-day one. Read your product's leaflet. |
Dose counts are the raw division and ignore dead space. Subtract roughly 10% if you draw with a detachable needle. Doses shown for illustration of the arithmetic only – they are not dose recommendations.
When to reorder
The number the calculator gives you is a run-out date, and a run-out date is only useful with a lead time subtracted from it. Order at weeks remaining minus your supplier's worst realistic delivery window, not at the point the vial looks low. For a pharmacy that is usually a few days; for anything shipped internationally, three to four weeks is the safe assumption, and customs delays are the normal failure mode rather than the exotic one.
The second-order problem is that a gap in supply is not just an inconvenience on an ester-based protocol – levels fall on the ester's own schedule, and a two-week gap on a long ester reads very differently from a two-week gap on a daily peptide. If you want to see what a gap would actually do to your levels, the half-life calculator models the decay.
Frequently asked questions
How long will my vial last?
Divide the total amount of drug in the vial by your dose to get the number of doses, then divide that by your injections per week. A 10 mL vial at 200 mg/mL holds 2,000 mg; at 100 mg twice a week that is 20 doses and about 10 weeks. Then check that answer against the vial's in-use limit once opened, because if the limit lands first it, not the volume, is what ends the vial.
How many doses are in a 10 mL vial of 200 mg/mL testosterone?
2,000 mg in total, so it depends only on the dose: 20 doses at 100 mg, 26 at 75 mg, 40 at 50 mg. Expect roughly 10% fewer in practice if you draw with a detachable needle, because 35 to 100 µL stays behind in the hub each time.
Why do I get fewer doses out of a vial than the calculator says?
Dead space, mostly. The volume left in the syringe hub and needle after injecting is drawn from the vial but never delivered, and with a luer-lock syringe and detachable needle that is around 70 µL per injection – 14 mg at 200 mg/mL. Rounding your dose up to the nearest syringe mark costs a little more. Vial overfill gives some of it back, which is why the shortfall usually lands near 10% rather than the full theoretical loss.
How long can you use a multi-dose vial after opening it?
The widely applied convention is 28 days from the first puncture, which is the CDC's injection-safety guidance for a punctured multi-dose vial unless the manufacturer specifies otherwise. It is a rule about preservative and contamination rather than a claim that the drug has broken down, and the label on a dispensed multi-dose vial may permit use until its printed expiry date instead. Follow your own label or your prescriber, not the strictest number you find online.
Does a bigger vial always work out cheaper?
Per mg, almost always. Per dose you actually inject, only if you finish it in time. A 10 mL vial discarded 60% full at an in-use limit costs more per delivered dose than a 2 mL vial you use completely, even though its price per mg looks far better. Work out cost per usable dose before buying the larger size.
How do I calculate cost per dose?
Vial price divided by doses per vial. A $60 vial giving 20 doses is $3.00 per dose, and at two injections a week that is $6.00 per week. If an in-use limit means you will only give 8 of those doses, the real figure is $7.50 per dose – divide by the doses you will use, not the doses the vial contains.
How many mg is 0.5 mL of 200 mg/mL testosterone?
100 mg. Concentration times volume: 200 mg/mL × 0.5 mL. On a U-100 insulin syringe that is the 50-unit mark, since 100 units is 1 mL.
When should I reorder?
At your run-out date minus the worst realistic delivery time, not when the vial looks low. A few days is usually enough for a pharmacy; assume three to four weeks for anything crossing a border. OptiPin projects the run-out date from your logged doses and warns you ahead of it.
Sources & further reading
- CDC – Injection safety: single-dose and multi-dose vial questions
- USP General Chapter <797> – sterile compounding and beyond-use dating
- OptiPin – Peptide storage and shelf life, for what actually degrades a reconstituted vial
- OptiPin – Peptide reconstitution calculator, for turning a vial into a syringe volume
Related tools
- Peptide reconstitution calculator – how much bacteriostatic water, and what to draw.
- Vial transition calculator – matching your dose when the new vial is a different concentration.
- Half-life calculator – what a supply gap does to your levels.
- TRT access and cost by country – what a vial costs where you are.