Insulin Day Supply Calculator
Calculate how many days your insulin vial or pen will last based on your current dose. Useful for prescription refill planning and travel preparation.
📅 Day Supply Calculator
Include all basal + all bolus doses.
Day Supply Estimate
(1 vial/pen)
(7-day buffer)
for 30 days
for 90 days
How to Use This Calculator
- Choose your vial or pen size (or enter a custom total in units).
- Enter your total daily dose — all basal plus all bolus units.
- Enter how many vials or pens you have.
- Read the result: days per container, total days, a refill-by date, and vials needed for 30 or 90 days.
Remember the 28-day in-use limit for opened insulin can shorten the usable supply at low doses, so always keep a buffer.
Insulin Supply Planning Tips
Day Supply Formula
Example: 1,000-unit vial (10 mL U-100) ÷ 40 units/day TDD = 25 days per vial. For a 90-day supply: 90 ÷ 25 = 3.6 → 4 vials needed.
Common Vial and Pen Sizes
| Format | Volume | Concentration | Total Units |
|---|---|---|---|
| Standard vial | 10 mL | U-100 | 1,000 units |
| Pen cartridge | 3 mL | U-100 | 300 units |
| Humalog U-200 KwikPen | 3 mL | U-200 | 600 units |
| Toujeo SoloStar | 1.5 mL | U-300 | 450 units |
| Humulin R U-500 vial | 20 mL | U-500 | 10,000 units |
Never wait until your last vial before refilling. Pharmacy stock issues, insurance delays, and travel disruptions can all cause supply gaps. Maintain at least a 7–10 day buffer. For international travel, carry more than needed and keep insulin in carry-on luggage (not checked bags where temperature extremes may degrade it).
Traveling With Insulin: Supply & Storage
Packing and airport security
Always carry insulin, pens, syringes, pumps and CGM supplies in your carry-on — the cargo hold can freeze and ruin insulin. Insulin and its supplies are allowed through security; declare them, and they're generally exempt from liquid limits in reasonable quantities. Bring a prescription or doctor's letter (especially for international travel) and split supplies between bags in case one goes missing.
Keeping insulin cool & crossing time zones
Use an insulated bag or a cooling wallet (e.g. a Frio-style pouch) in hot climates, but don't let insulin freeze against ice packs. For long flights across several time zones, the timing of long-acting basal may need adjusting while rapid-acting insulin is still given with meals — plan this with your care team before you go.
Frequently Asked Questions
How long does a vial of insulin last?
Divide the vial's total units by your daily dose. A standard 1,000-unit (10 mL U-100) vial at 40 units/day lasts 25 days. Note that once opened, most insulin should be discarded after about 28 days even if units remain.
How many insulin vials do I need for 90 days?
Divide 90 by the number of days one vial lasts, then round up. If a vial lasts 25 days, 90 ÷ 25 = 3.6, so you need 4 vials for a 90-day supply.
Does opened insulin expire before it runs out?
Often, yes. Most opened vials and pens are good for about 28 days at room temperature (some up to 42–56 days), regardless of how many units are left. Always follow the package insert and discard on time — see our storage & expiration guide.
When should I refill my insulin?
Keep at least a 7–10 day buffer. Order your refill while you still have a week or more of supply to absorb pharmacy stock issues, insurance delays, or travel disruptions.
Can I take insulin through airport security?
Yes. Insulin, pens, syringes, pumps and CGMs are permitted in carry-on bags. Declare them at the checkpoint, keep them with the pharmacy label, and bring a doctor's letter or prescription if you can. They're generally exempt from the usual liquid limits in reasonable quantities — keep them in your carry-on, never checked luggage.
How much extra insulin should I pack for a trip?
A common rule is to pack about twice what you expect to need, and split it between two bags in case one is lost. Add extra pen needles or syringes and spare pump or CGM supplies. Account for delays, time-zone changes and the chance of a damaged vial.
Source
- American Diabetes Association. Standards of Care in Diabetes — 2024.
- Insulin package inserts (in-use storage limits by brand).
Last reviewed: June 2025