a patient is prescribed lantus 30u subQ tid. how long will one vial last

i calculated 11 days is that correct?

No, the calculation is not correct.

If the patient is taking Lantus 30u subQ tid (three times daily), that would be a total of 90 units per day.

Assuming one vial contains 1000 units (the most common size), then one vial would last for approximately 11 days and 1 hour (1000 units divided by 90 units per day).