Question About Prescription Due Date After Filling A 28-Day Supply

In our latest question and answer, the pharmacist discusses when a prescription refill is due after filling a 28-day supply.


I recently had a change to my prescription regarding how many days the supply is and so on. I had my script filled on 11/18/2022. My script used to be a 30-day supply but now is a 28-day supply. It is an opiate for chronic pain. Do I call it in on 12/14/2022? They say 2 days before it is due, if it is 28 days, that would be 12/16/2022. I want to make sure I’m addressing this way ahead of time. Thank you very much.

Asked by Christy197980 On Nov 29, 2022

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Nov 29, 2022
Last updated Nov 29, 2022

Key points

  • There is often confusion surrounding when a prescription refill is 'due'. It can vary based on the laws in your area and the specific policies of your pharmacy.
  • In general, a prescription refill is 'due' on the first day you would have no medication to take your next dose.


You're spot on with the date calculation you wrote in your question.

If you filled a 28-day supply of your prescription on 11/18/2022, you are 'due' for your next fill on 12/16/2022. Since your pharmacy has indicated that you can fill 2 days early from your 'due date', that would be 12/14/2022.

Prescription 'Due' Dates

There is often a lot of confusion surrounding prescription due dates, and when something can be filled. This generally is more of a problem with controlled substances due to ambiguity with federal and state laws, as well as individual pharmacy policies.

This is a topic we have written about several times in the past (here is a description of how your pharmacist calculates day supply and another example of a specific situation regarding controlled substances).

I think the easiest way to describe when you are legally 'due' for a prescription refill is that it is the first day in which you will not have a dose of medication to take.

For example, if you received a 7-day supply of medication on 11/7/2022, a Monday, you are 'due' for a refill on 11/14/2022, the next Monday, as that would be the first day in which you have no medication left to take.

Now, you may be able to fill your medication a little early from the actual 'due' date, but this will vary on several different factors. I always highly recommend talking directly to your pharmacy about when you can refill your medication.

Due Date After A 28-Day Supply Fill

In your example, you filled a 28-day supply prescription on 11/18/2022. The first day you would be without medication (assuming you took it consistently), would be 12/16/2022. That is your 'due' date.

In the calendar below, I list off the days (I am assuming one dose per day, but the concept is applicable regardless of how many doses you take per day) showing the due date of 12/16/2022.

Prescription 28 day Due Date calendar

If your pharmacy said they will fill it two days early, as you stated, that would be 12/14/2022.

Final Words

I really try to emphasize with these types of questions the importance of talking to your pharmacy.

There are a lot of factors that can influence prescription fill dates.

As one example, in New York State, the law states you can fill a controlled substance as long as you have no more than a 7-day supply on hand, but your prior fill history, and the policies of your prescriber and pharmacy, can alter the day you can actually fill your medication.

I hope you found this helpful! Please feel free to write back out anytime.

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at! You can also connect with Dr. Brian Staiger on LinkedIn.

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