Vial duration calculator

Vial duration is the answer to one practical question: at my current dose and frequency, how long will one vial last before I need to open a new one? It is the number that drives refill timing — when to reorder, when to thaw a backup vial, when to plan around a trip — and it is the most under-tracked number in peptide use, because most people only notice they are running low when the vial is already nearly empty.

The calculation itself is simple. Total milligrams in the vial divided by milligrams per dose gives the total number of doses the vial holds. Total doses divided by doses per week gives the number of weeks the vial will last. Both halves of that math are exact, but the result is rounded down to whole doses because a partial draw at the very bottom of a vial is rarely usable.

Doses per vial — which appears on the reconstitution calculator — only answers half the question. It tells you how many injections fit inside the vial, but not how long that supply will actually last in real life. A vial that holds 40 doses lasts 40 weeks at one injection per week, but only 20 weeks at twice-weekly dosing and only about 5.7 weeks if used every day.

Vial duration takes the missing variable — frequency — and converts the dose count into a calendar-time estimate. That estimate is what is actually useful for planning, because shipping windows, refrigeration, and travel all happen on calendar time, not on dose counts.

The calculator deliberately rounds total doses down to a whole number. If the math says 42.7 doses, it shows 42, because the 0.7 of a final draw at the bottom of the vial is usually too little fluid to pull cleanly into a syringe at the angle the needle reaches. Counting it would make the duration estimate optimistic by exactly one dose, which is the difference between running out exactly when planned and running out one injection early.

The same logic does not apply to the weeks number, which is shown as a real-valued estimate. A duration of 5.7 weeks is more useful than rounding to 5, because the half-week tells you whether the next vial needs to arrive at the start or the middle of the sixth week.

Most peptide refill mistakes come from one of two patterns. The first is ordering too late, because no one was tracking the dose count and the vial ran out faster than expected. The second is ordering too early, because someone manually counted a few doses and overestimated how much was left, ending up with backstock that aged out before it could be used.

Both mistakes go away when the vial duration is computed up front and the refill is timed against it. A vial that the calculator says will last 8 weeks should trigger a reorder check around week 6, not week 8. That two-week buffer covers shipping, cold-chain handling, and the chance that one dose got skipped or drawn slightly higher than planned.

Tracking the actual dose log against the predicted duration is the other half of the workflow, and it is the half a calculator alone cannot do. Logging in Peptide Pilot ties every recorded dose to the specific vial it came from, so the remaining-dose estimate updates in real time as the vial gets used, instead of being a one-shot calculation from the day the vial was opened.

The vial duration calculator assumes a regular weekly cadence. Most peptide protocols fit cleanly into that — once a week, twice a week, every other day rounded to roughly 3.5 doses per week. Where the math gets less clean is when the schedule is intentionally irregular: a loading phase followed by a maintenance phase, or a cycle on followed by a cycle off.

The cleanest workaround is to compute duration for each phase separately and add the results. A vial used for two weeks at a daily dose and then the rest at a twice-weekly dose is two duration calculations stacked end to end, not one average. Trying to pick a single 'average' frequency for an irregular schedule almost always produces a duration estimate that is wrong in both directions over the life of the vial.

For protocols that include planned skipped weeks, treat each on-week as a full-frequency week and ignore the off-weeks for the dose-counting math; then add the skipped weeks back into the calendar duration at the end. The vial does not deplete during off-weeks, so they extend wall-clock time without adding doses.

Most people who run more than one peptide hit the same problem at some point: each vial has its own duration, but the reorder cycles drift relative to each other and end up landing in the same week, which makes refrigerator inventory awkward and shipping costs add up.

The fix is to compute vial duration for each peptide separately, mark the predicted end date on a shared calendar, and stagger reorders so deliveries land at least a week apart. The calculator will not do the calendar math for you, but its outputs are the inputs that workflow needs.

Tracking apps like Peptide Pilot show all active vials on one screen with their predicted depletion dates highlighted. That is mostly a quality-of-life feature on top of the same arithmetic — the calculator answers the question for one vial; the app answers it for all of them at once and triggers reminders without anyone having to keep a calendar manually.

The duration estimate assumes the dose drawn is exactly the dose typed and that no liquid is wasted. In reality, small amounts of solution stay behind in the syringe hub, in the needle dead space, and on the rubber stopper after each draw. Across an entire vial those losses can add up to roughly one extra dose's worth of fluid, which is part of why rounding total doses down is more honest than rounding to nearest.

The estimate also cannot account for missed doses, doubled doses, or unplanned changes mid-protocol. None of those break the math — they just mean the prediction made on day one diverges from reality by the time the vial is half empty. A logging app continually rebases the estimate against actual recorded doses, which is the only way to keep the prediction useful for the entire life of the vial.