We need insulin on a daily basis for a type II diabetic for whom the oral meds are ineffective. Our insurance encourages mail order of 3 month supply for the price of 2 months co-pay. Two months after your last order, you are allowed to refill. We do this all the time, and thus have built up and keep a minimum 3 month supply on hand in the fridge. The prescription is valid for one year. Just watch expiration dates and use on a first in first out basis. When traveling on vacation, we take a supply for at least twice the length of time of the projected time away from home. Also having a couple of spare original prescriptions with you when traveling is a good idea.