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When will your vial run out?

Enter what's left in the vial, your dose, and how often you dose. Get a projected run-out date back — and a reorder-by date if you tell it your lead time. Nothing to install, no account, no compound list to pick from.

This calculator performs calculations on numbers you enter. It contains no medical information and provides no guidance. It does not supply, suggest, rank, or evaluate any compound, dose, or range — and it never will. Not a medical device. Consult a licensed professional for any medical decision.

Enter your numbers

Whole days. 1 for daily, 7 for weekly, and so on.

How many days ahead your supplier needs. Leave blank to skip the reorder-by date.

Clear all fields

Result

Projected run-out date
—
assuming every scheduled dose is taken on time
Doses remaining —
Reorder by —

How this is calculated

The method

Starting from today, the calculator walks forward one day at a time at the frequency you entered, subtracting your dose from what's remaining on every day it's due, and reports the day the vial runs out — the same engine VialMath itself uses for every vial on record, not a separate estimate. Doses remaining is the vial amount divided by your dose, full doses only. The reorder-by date, if you gave a lead time, is simply the run-out date moved back by that many days.

Worked example

You have 6 mg remaining. Your dose is 0.5 mg, taken every 3 days. Doses remaining: 6 mg ÷ 0.5 mg = 12. Counting forward from today every 3 days, the 12th dose lands 3 × 11 days out — 33 days from today. With a 5-day reorder lead time, the reorder-by date is 33 − 5 = 28 days from today. Every number above is checkable on a calculator.

This calculation is correct right now. What happens when the dose, schedule or vial changes?

VialMath keeps your calculations, schedule, inventory and history connected.

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The questions people actually ask

How do I calculate when a vial will run out?

Divide what's left by your dose to get doses remaining, then space those doses out at your dosing frequency, starting today. The calculator above does that day-by-day rather than as a single average, so it stays exact even when the amount left isn't a clean multiple of the dose.

What is a reorder-by date?

The run-out date, moved earlier by however many days your supplier needs to get you a new vial — so the reorder happens before the old one is empty, not after.

Does this account for missed or extra doses?

No — it projects forward from the amount you enter today, assuming every scheduled dose from here is taken on time. A missed or extra dose changes how much is actually left; re-enter the current amount and the projection updates.

Can it handle an on/off cycle, like 5 days on and 2 days off?

This free tool assumes one steady "every N days" cadence. On/off cycles, weekday-only schedules, and more than one dose a day are handled in the full VialMath app, which already runs this exact projection against a real schedule.

Do I have to redo this every time I log a dose?

Not in the full app. Log a dose once and the run-out date and reorder-by date recompute on their own — nothing to re-enter by hand.

Told when it changes

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