Determining your next refill date is now easier than ever. Our free and accurate 90-day prescription refill calculator takes out all the math and guesswork you’d have engaged yourself in. To use our calculator, simply enter the fill date or the date you took your first dose and then click on the calculate next refill button. The calculator will do the maths and then display the date for your next refill. It is that simple!

How to Calculate a 90-Day Prescription Refill Date

It is quite easy to calculate your next 90-day prescription refill date. This can be done in 3 simple steps.  

1. Write down the date when you take the first dose from your new 90-day supply. This will serve as the starting point for calculating your refill date.
2. Count forward 89 days from the date of your first dose. This 89th day will be the date when you need to take the final dose from your current 90-day supply.
3. Add one day to the date of your final scheduled dose to determine the start of your next 90-day refill period. For example, if your last dose from the initial 90-day supply is September 12th, then September 13th marks the beginning of your next eligible 90-day refill period.

These two examples help illustrate the calculation:

Example 1:

• You start a new 90-day supply of medication on January 1st.
• Counting forward 89 days from January 1st, your final dose from this supply will be on March 30th.
• Add one day to March 30th, and you can refill your next 90-day supply on March 31st.

Example 2:

• You begin a new 90-day supply of medication on May 15th.
• Counting forward 89 days from May 15th, your final dose from this supply will be on August 12th.
• Add one day to August 12th, and you can refill your next 90-day supply on August 13th.

Bear in mind that each dispensed 90-day prescription supply is intended to provide a 90-day supply of medication. The final dose date signals the end of the 90-day cycle, and the very next day starts the clock for the following 90-day window when you can receive your next 90-day refill.