OptiPin
Vial transition calculator
New vial, different concentration, same dose. Work out the units to draw so the switch does not quietly become a double dose, and split a dose across the last of the old vial and the first of the new one.
Matching your usual doses on the new vial
What each of your old unit counts becomes at the new concentration. If the new column is smaller than the old one, the new vial is stronger and drawing your usual amount would overdose you.
| Dose | Old vial | New vial | Change |
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OptiPin knows which vial you are on
Log a new vial with its strength and water volume and OptiPin recalculates your units automatically, so a concentration change never silently carries over from the vial before it.
Download on the App StoreHow to use this calculator
Why switching vials is the risky moment
Unit counts become muscle memory. After a month of drawing to the same line on the barrel you stop reading it as a volume. The number is remembered, the concentration behind it is not, and a new vial breaks the link without any visible sign.
Doubling is the common failure. Going from a 5 mg to a 10 mg vial and reconstituting both with the same water halves the units you need. Draw your old number and you have taken exactly twice your dose. If that has already happened, the reverse dose calculator will tell you how much.
You can dilute your way back. If a stronger vial gives you an awkward draw, add proportionally more water: 10 mg in 4 mL matches 5 mg in 2 mL exactly, and your unit count carries over untouched.
Do not let a part-vial push you off dose. Rounding a short final dose down "just this once" is how a titration quietly stalls. Splitting the dose across two vials keeps the schedule intact, and both draws go into the same syringe.
Common questions
How do I switch to a vial with a different concentration?
Keep the dose in milligrams fixed and recompute the units. Divide your dose by the new concentration and multiply by 100 for a U-100 syringe. 1 mg from a 2.5 mg/mL vial is 40 units, and the same 1 mg from a 5 mg/mL vial is 20 units.
Can I mix the last of one vial with a new one?
You can draw from both into the same syringe to make up a single dose. What you should not do is pour one vial into the other: you lose track of the resulting concentration and combine two different beyond-use dates into one container.
How much water should I put in the new vial?
If you want your existing unit count to keep working, scale the water with the strength: double the milligrams, double the water. Otherwise pick the volume that gives a comfortable draw.
What if the new vial is a different brand or batch?
Treat it as a new concentration regardless of what the label suggests. Peptide vials from different suppliers vary in fill, and a 10 mg label is a nominal figure rather than a guarantee.
Does the leftover in the old vial count as wastage?
Some of it always will. Syringe and needle dead space holds a small volume you cannot recover, so plan on the last draw being slightly short.