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Prescription arithmetic

Vial supply tracker

See how many doses, and roughly how many days, are left in a vial. Pure arithmetic, no dosing suggestion.

mL
mg/mL
mg

For education only. This tool verifies arithmetic on a prescription you already have. It does not suggest a dose or refill schedule.

How this calculator works

Total medication in the vial equals its volume in mL multiplied by its concentration in mg/mL. Subtracting what you've already drawn, then dividing by your per-injection dose, gives the number of full doses left. If you also enter your injection frequency, dividing remaining doses by that frequency and multiplying by seven estimates days of supply.

Why estimates can run a little high

Vial stoppers and needle dead space can account for a small amount of unusable medication, so your real supply may run out a few days sooner than a pure arithmetic estimate suggests. Treat the result as a planning estimate, not an exact countdown.

Frequently asked questions

How do I calculate how many doses are left in a testosterone vial?

Multiply the vial's total volume in mL by its concentration in mg/mL to get the total milligrams in the vial. Subtract whatever you have already used, then divide the remaining milligrams by your per-injection dose to get the number of doses left.

How do I know how many days my vial will last?

Divide your remaining doses by how many injections you take per week, then multiply by seven. This tool does that calculation automatically once you enter your injection frequency.

Why does this matter?

Running out of medication unexpectedly, especially around a new prescription or refill, can disrupt a dosing schedule. Knowing roughly how many days of supply are left gives you time to request a refill before that happens.

Does this tool account for any medication wasted during a draw?

No. It assumes every milligram in the vial is eventually used. In practice a small amount is sometimes lost to the needle or vial stopper, so real supply may run out slightly sooner than this estimate.

This tool is for general educational purposes and is not medical advice. It does not recommend a dose, injection frequency, or refill timing. Follow your prescriber's instructions.

Method

Standard volume and concentration arithmetic (volume × concentration = total mg; remaining mg ÷ dose = doses left). This tool performs no pharmacology modeling and cites no dosing guideline, since it does not recommend a dose.