Insulin Vial Calculator
Find out how long an insulin vial lasts and how many vials you need for a given period — from your daily dose, vial size, and concentration, including the 28-day discard rule.
e.g. 90 days for a quarterly refill.
How to Use This Calculator
- Enter your total daily dose in units per day.
- Enter the vial size (commonly 10 mL) and select the concentration (U-100 is standard).
- Enter the days to cover — e.g. 90 for a quarterly refill.
- Read the result: how many vials you need and how long one vial lasts.
This is a supply-planning estimate. If a vial would last beyond about 28 days at your dose, the in-use limit — not the volume — may decide how many you actually use.
How to Work Out Vial Supply
Each vial holds a fixed number of insulin units: its volume multiplied by its concentration. Divide that by your daily dose to see how many days a vial lasts, then divide your coverage period by that figure to find how many vials you need.
Example: a 10 mL U-100 vial holds 1000 units. At 45 units/day it lasts ~22 days, so 90 days needs ⌈90 ÷ 22⌉ = 5 vials.
Units per Vial by Concentration (10 mL)
| Concentration | Units in a 10 mL vial |
|---|---|
| U-40 | 400 units |
| U-100 | 1,000 units |
| U-200 | 2,000 units |
| U-500 | 5,000 units |
Vial sizes vary (commonly 3 mL or 10 mL). Always check the label for both the volume and the concentration.
Insulin Storage: Shelf Life & the 28-Day Rule
Unopened vs in-use storage
Unopened insulin stays in the fridge at 2–8 °C (36–46 °F) and is good until the printed expiry date. Once opened or in use, most insulin can be kept at room temperature — generally below 30 °C (86 °F), away from heat and direct light — and is discarded after a set number of days regardless of how much is left.
In-use limits vary by product
The common in-use limit is 28 days (for example glargine/Lantus and most rapid-acting vials), but some long-acting analogues allow longer — detemir up to ~42 days and degludec (Tresiba) and glargine U-300 (Toujeo) up to ~56 days. Always check your specific product's label or ask your pharmacist.
Never use insulin that has been frozen or exposed to high heat, or that looks clumped, frosted or discolored.
Frequently Asked Questions
How long does a 10 mL vial of insulin last?
A 10 mL U-100 vial holds 1,000 units. Divide by your daily dose: at 50 units/day it lasts about 20 days; at 25 units/day about 40 days. Remember many vials should be discarded ~28 days after first use.
How many insulin vials do I need for 90 days?
Divide 90 by how many days one vial lasts and round up. At 45 units/day with 10 mL U-100 vials (1,000 units each, ~22 days), you'd need 5 vials for a 90-day supply.
Does the 28-day rule change how many vials I use?
It can. If your dose is low enough that a vial would last beyond about 28 days, you may discard it before it's empty. In that case the in-use limit, not the volume, determines real-world usage. Confirm the exact limit for your insulin.
What's the difference between vials and pens for supply?
Vials hold more units but are drawn with a syringe; pens are pre-filled (commonly 3 mL = 300 units at U-100). For pens, see our pens per month calculator and day supply calculator.
Can insulin be left out of the fridge?
Yes, once it's in use. The vial or pen you are currently using is usually kept at room temperature (below about 30 °C / 86 °F), which makes injections more comfortable, and discarded after its in-use limit. Spare, unopened insulin should stay refrigerated until you start it.
What happens if insulin freezes or gets too hot?
Both damage it. Freezing or high heat breaks down insulin so it no longer works reliably, even if it looks normal — and it should be discarded. Don't leave insulin in a hot car or freezer; if it has been frozen, looks clumped, frosted or discolored, replace it.
Sources
- Manufacturer prescribing information for insulin vials (in-use storage and discard limits).
- American Diabetes Association. Insulin storage and safety guidance.
Last reviewed: June 2025