Insulin Vial Calculator
Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM — October 2026
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.
A 10 mL vial of U-100 insulin contains 1,000 units, so at 40 units a day it should last twenty-five days. Whether it actually does depends on a rule that has nothing to do with how much is left.
Once opened, insulin has a limited in-use life — commonly 28 days at room temperature, though it varies by product. After that it should be discarded regardless of remaining volume, because potency degrades and a dose that worked in week one may not in week six. For anyone using modest daily doses, this rule, not the unit count, is what determines how many vials a year they need.
The surprising result: lower-dose users often waste more insulin than higher-dose users, because they discard half-full vials on schedule.
Storage handling matters as much as the calendar. Unopened vials keep until their printed expiry if refrigerated; heat, freezing and direct sunlight all shorten that considerably, and insulin that has frozen should never be used even after thawing.
The calculator below works out how long a vial lasts and how many you need. Beneath it you will find units per vial by concentration and the storage rules in full.
How to Use the Insulin Vial 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.
How many doses are in a vial?
Divide the units in the vial by the units in one dose. A 10 mL U-100 vial holds 1,000 units, so at 8 units per mealtime dose it gives 125 doses, and at 25 units of basal once a day it gives 40 doses. Syringe users lose almost nothing to priming, unlike pen users, who prime 2 units before each injection. To turn a unit dose into the volume you draw up, use the insulin units to mL calculator.
Exam-style example: a 10 mL vial at two daily doses
A patient injects 40 units every morning and 10 units at bedtime from a 10 mL vial of U-100 insulin. How many days will the vial last?10 mL × 100 units/mL = 1,000 units40 + 10 = 50 units/day → 1,000 ÷ 50 = 20 days
Twenty days falls inside a 28-day in-use limit, so the volume, not the calendar, decides when this vial runs out.
Units per Vial and In-Use Days by Product
Every human-use insulin vial sold in the US today is U-100, so a 10 mL vial holds 1,000 units and a 3 mL vial holds 300 units. The concentrated insulins (U-200, U-300 and U-500) come only in pens. The in-use limit is what differs between products.
| Vial | Units | Discard after opening |
|---|---|---|
| Humalog, NovoLog, Admelog, Apidra, Fiasp, Lyumjev (10 mL) | 1,000 | 28 days |
| Lantus, Semglee and other glargine U-100 (10 mL) | 1,000 | 28 days |
| Tresiba U-100 (10 mL) | 1,000 | 56 days |
| Humulin R, Humulin N, Humulin 70/30 (10 mL) | 1,000 | 31 days |
| Novolin R, Novolin N, Novolin 70/30 (10 mL) | 1,000 | 42 days |
| 3 mL U-100 vials (some rapid-acting and Humulin products) | 300 | Same as the 10 mL vial |
| Veterinary U-40 vials, e.g. Vetsulin, ProZinc (10 mL) | 400 | Per the veterinary label |
Levemir vials left the US market at the end of 2024. Always check the label on the vial in your hand for volume, concentration and in-use limit.
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 FDA states that most insulin stays effective for up to 28 days unrefrigerated at 59–86 °F. Labels then set each product's exact limit: 31 days for Humulin vials, 42 days for Novolin vials, and 56 days for Tresiba (vial and pen) and Toujeo pens. Check your own 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.
Vials are one piece of a refill plan. Pens, pumps and dose math live together in our insulin supply and dosing calculators.
Frequently Asked Questions: Insulin Vial Calculator
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.
How many units are in a vial of insulin?
A standard 10 mL vial of U-100 insulin holds 1,000 units (10 mL × 100 units/mL). A 3 mL U-100 vial holds 300 units. Veterinary U-40 vials such as Vetsulin hold 400 units in 10 mL. In the US, U-200, U-300 and U-500 insulins come only in pens, not vials.
How many doses are in a vial of insulin?
Divide the units in the vial by your dose. A 1,000-unit vial gives 100 doses of 10 units, 125 doses of 8 units, or 40 once-daily doses of 25 units. If those doses stretch past the product's in-use limit, usually 28 days, discard the vial on that date even if insulin remains.
Sources
- U.S. Food and Drug Administration. Information Regarding Insulin Storage and Switching Between Products in an Emergency. Link — source of the 28-day, 59–86 °F rule and the frozen-insulin warning.
- Novo Nordisk. Filling Tresiba prescriptions: what you need to know (10 mL U-100 vial, 1,000 units, 56 days in use). Link
- Manufacturer prescribing information for Humulin, Novolin, Humalog, NovoLog and Lantus vials (in-use storage and discard limits).
Written by Ryan Mitchell · Last updated: October 2026