Insulin & GLP-1 days supply calculator
Pharmacy systems often can't work out days supply for “10 units daily.” Pick the pen or vial, enter the dose, and see the days supply with the math shown. Switch to How many to give to get boxes and pens for 30 or 90 days.
Any number, including 5 or more.
5 pens in a box.
Package details
Filled in from the product labeling. Pack sizes vary by NDC, so change these to match the box you have.
Default 300
Default 5
Default 28
Days supply
28 days
- 10 units × 1 a day = 10 units a day
- 300 units per pen ÷ 10 a day = 30 days per pen
- Once opened it must be thrown out after 28 days, so each pen counts for 28 days
- 1 pen × 28 days = 28 days
Worked examples
Lantus SoloStar, 10 units daily, 1 pen
300 ÷ 10 = 30 days, but the pen is thrown out 28 days after opening = 28 days
Lantus SoloStar, 30 units daily, 1 box of 5 pens
1,500 units ÷ 30 a day = 50 days
U-100 pens, 40 units twice daily, 90 days needed
300 ÷ 80 = 3.75 days a pen → 24 pens = 4 boxes + 4 pens
Ozempic 1 mg weekly, 1 pen
4 weekly doses × 7 days = 28 days
Mounjaro, 1 box of 4 single-dose pens
4 weekly doses × 7 days = 28 days
Victoza 1.2 mg daily, 3-pen pack
18 mg ÷ 1.2 = 15 days a pen × 3 = 45 days
How insulin days supply works
- Find the units in each pen or vial: mL × strength. A 3 mL U-100 pen has 300 units; a 10 mL vial has 1,000.
- Find the units used a day: units per dose × doses a day.
- Divide to get days per pen, then multiply by the pens dispensed.
- Check the in-use limit. If a pen would last longer than its discard date after opening, it only counts for that many days.
Easy places to slip
- U-200 and U-300 pens hold more units per mL than U-100. A Toujeo SoloStar (1.5 mL of U-300) holds 450 units.
- Low doses hit the in-use limit first. Ten units a day from a 1,000-unit vial is not 100 days if the vial is thrown out after 28.
- Priming (the 2-unit safety test before each shot) adds up. Some pharmacies and plans count it; turn it on if yours does.
- Weekly GLP-1 pens are counted in doses, not units: four weekly doses is 28 days.
Pack sizes and in-use limits come from the product labeling and can change. Check the box in hand, and follow your pharmacy's policy, the plan's rules and the pharmacist for the days supply you bill.
Patient asking how long it can stay out of the fridge?
See the out-of-fridge guide for insulins, GLP-1 pens and antibiotic suspensions.
Studying for the PTCE?
Days supply is on the exam. Gutta's Order Entry lessons teach it with worked examples, then quiz you until it's automatic.
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