30 Day Refill Calculator
Never get caught without your next refill again
Pharmacies and insurers work in days supply and early refill windows, not vague guesswork, and this calculator speaks that same language. Enter your last fill date and supply length, and it works out exactly when you become eligible to refill, when your current supply actually runs out, and what your refill schedule looks like for months ahead.
Enter your fill date to see your supply visually
Step 1 · Your fill details
Enter your last fill date and supply length
These two numbers are all a pharmacy actually needs to schedule a refill, and they're all this calculator needs too.
The date you picked up or received your most recent supply. This can be any past date, it doesn't have to be recent.
Defaults to today, but you can move this to check your refill status on any other date too.
How many days one fill is meant to last. Standard retail pharmacy fills are usually 30 days, while mail order plans often use 90.
Turn this on if you'd rather work from how many units are in the bottle and how many are used per day, instead of typing days supply directly.
Most insurance plans allow a refill once a set percentage of the current supply has been used, rather than making you wait until the very last day.
Step 2 · Your refill status
Planning ahead
Your next six refill dates
Assuming you refill right at your early eligibility window each time, here's what your schedule looks like stretching forward.
Worth comparing
30, 60, and 90 day supplies side by side
Switching supply lengths changes more than convenience, it changes how many trips to the pharmacy or mail order shipments you're dealing with across a year. Here's the same medication schedule under each common option.
| Supply length | Refills per year | Pharmacy contacts per year |
|---|
How this works
The scheduling logic behind your dates
Every date here comes from direct calendar arithmetic under the Gregorian calendar, the civil calendar referenced by ISO 8601 for exchanging dates. The scheduling logic mirrors how most pharmacy systems and insurance plans actually track fills, using two figures: total days supply and the percentage of that supply that must be used before a refill is authorized.
Calculating days supply from a bottle count
When you enter a bottle count instead of typing days supply directly, the calculator divides the total units in the bottle by how many units are used each day, rounding down to a whole number of days, since a partial day of medication doesn't count as a full day of coverage.
Working out the early refill window
Multiplying your total days supply by your chosen percentage gives the number of days that must pass before a refill becomes authorized. For a 30 day supply at an 80 percent early refill rule, that's 24 days, meaning a refill becomes available six days before the bottle would actually run out.
For example, someone who filled a 30 day supply on the first of a month, under an 80 percent early refill rule, becomes eligible to refill on day 24 and would fully run out on day 30 if no refill happened. Building in that six day cushion is exactly why insurance plans set the window early rather than right at the last dose.
Common questions
Frequently asked questions
How is a 30 day refill date calculated?
The calculator adds your days supply to your last fill date to find when the supply runs out, then applies your early refill percentage to that same supply length to find the earlier date when a refill typically becomes available.
What does an early refill window actually mean?
It's the point at which a pharmacy or insurance plan will authorize a new fill before the current one is completely gone, usually expressed as a percentage of the supply that needs to be used first, such as 75 or 80 percent.
Can I refill before my insurance allows it?
That depends entirely on your specific plan and pharmacy, and this calculator can't override those rules. It simply estimates the same kind of percentage based window that most plans use, so you can plan ahead of time rather than being surprised at the counter.
How do I calculate days supply if my prescription isn't a standard amount?
Switch on the bottle count option and enter the total units in the container along with how many are used per day. The calculator divides one by the other to get an accurate days supply figure instead of assuming a standard 30 day count.
Does a 90 day supply mean fewer trips to the pharmacy?
Yes, a 90 day supply typically means roughly four fills a year instead of twelve, which is exactly why the comparison table above shows refill frequency side by side across the common supply lengths.
Does this calculator work the same way outside the United States?
The date math and scheduling logic work anywhere, since they're based on standard calendar arithmetic. Specific early refill percentages and standard supply lengths do vary by country and insurance system, which is why both are fully adjustable here rather than fixed.