It also discusses how to override this rejection with a few of the frequently used insurance companies. Insurance companies will usually allow a refill on a prescription once approximately 75% of the previous fill has been used up. This is typically close to 7 days early on a fill of a 30-day supply of a medication. On a 90-day supply, usually insurance companies will allow the prescription filled 21 days early. Some insurance companies allow pharmacy staff to enter an override code, indicating that there was a need for either a vacation override or dosage increase override.