Estimate prescription refill due and earliest request dates from your last fill date, days supply, and common 75%, 80%, or 85% policy presets.

Prescription Next Refill Date Calculator

Estimate due and earliest refill dates using common rule-of-thumb timing (rules vary by plan, pharmacy, medication, and whether the date is based on fill vs pick-up).

Note: This is a planning estimate. Always confirm with your pharmacy/plan for controlled meds, vacation overrides, mail-order timing, and pickup vs fill date rules.

Important: This tool provides estimates for informational purposes only and cannot determine insurance coverage or guarantee refill eligibility/dispensing quantity. Do not change how you take a medication based on this tool; confirm timing, quantity, and refill rules with your pharmacist/insurer and your prescriber (especially for controlled substances and medications with special dispensing rules).

28 Day Prescription Refill Formula

The following formula is used to estimate the number of refills needed when each fill provides a 28‑day supply. (A “refill” is an additional fill after the first fill.)

R = \max\!\left(\left\lceil \frac{D}{28} \right\rceil - 1,\; 0\right)

Variables:

  • R is the number of refills needed (not counting the first fill)
  • D is the total number of days the prescription is needed for

To calculate refills for a 28‑day supply, first compute the number of 28‑day fills needed: fills = ⌈D/28⌉ (round up to a whole fill). Then subtract 1 because the first fill is not a “refill.” If this results in a negative number (for example, D ≤ 28), use 0 refills.

What is a 28 Day Prescription Refill?

A 28‑day prescription fill means the pharmacy dispenses enough medication to last 28 days (a 28‑day “days supply”) when taken as directed. The prescription itself may include zero or more authorized refills, allowing the same prescription to be dispensed again without requiring a brand‑new prescription each time. A new prescription is generally needed only when no refills remain, the prescription expires, or the prescriber requires a new order.

How to Calculate 28 Day Prescription Refill?

The following steps outline how to calculate the number of refills needed for a 28 Day Prescription Refill.

  1. First, determine the total number of days the prescription is needed for (D).
  2. Next, calculate the number of 28‑day fills needed: fills = ⌈D/28⌉ (round up to a whole fill).
  3. Finally, calculate the number of refills needed: R = fills − 1 (minimum 0).
  4. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Total number of days the prescription is needed for (D) = 84

Fills needed = ⌈84/28⌉ = 3

Refills needed (R) = 3 − 1 = 2