What Is the Prescription Refill Date Calculator?
This tool estimates how long a medication supply will last and the date you will need a refill. Enter the total quantity dispensed (number of pills, tablets, or units), how many doses you take per day, and the date you started the prescription. The calculator works out your days supply and projects the date your supply runs out.
How to Use It
Provide three things: the total quantity you received, the doses per day you take, and the start date. Optionally set a reminder lead time so you know how many days ahead to request a refill. The result shows the run-out date plus a suggested reminder date.
The Formula Explained
Days supply is simply quantity divided by daily doses: \( \text{Days Supply} = \text{Quantity} \div \text{Doses per day} \). The refill (run-out) date adds the whole number of supply days to your start date. We use whole days because a partial day still leaves you needing the next dose. The reminder date subtracts your chosen lead time from the run-out date.
$$\begin{gathered} \text{Refill Date} = \text{Start Date} + \left\lfloor \text{Days Supply} \right\rfloor \\[1.5em] \text{where}\quad \left\{ \begin{aligned} \text{Days Supply} &= \dfrac{\text{Quantity}}{\text{Doses/Day}} \\ \text{Start Date} &= \text{Start Date} \\ \text{Reminder Date} &= \text{Refill Date} - \text{Lead Days} \end{aligned} \right. \end{gathered}$$
Worked Example
You receive 90 tablets and take 3 per day, starting on 2024-01-01. Days supply = \( 90 \div 3 = 30 \) days. Adding 30 days to January 1 gives a refill date of 2024-01-31. With a 5-day reminder lead, you would aim to refill by 2024-01-26.
FAQ
Does it account for missed doses? No — it assumes you take every scheduled dose exactly as entered. Skipped doses extend your supply.
What if I take half doses? Enter the actual number of units consumed per day, including fractions like 0.5.
Is this medical advice? No. This is an estimate for planning refills. Always follow your pharmacist's and doctor's instructions and the label.
