How to use the supply run-out and refill date calculator
- Enter the number of doses on hand, such as tablets, capsules or doses.
- Enter the doses per day. Use 0.5 for one dose every other day.
- Enter the first day of this supply and the days needed to refill, including mail or pharmacy time.
- Read how many days the supply covers, the first day you would be short, and the date to reorder.
Formula
full days covered = floor(doses on hand / doses per day)
first day short of a dose = first day + full days covered
reorder by = first day short - days needed to refill
The doses left over after the full days are shown. A supply that does not divide evenly leaves a partial day, which is not counted as a covered day.
30 tablets, one a day
Starting on March 2, 2026 with 30 tablets and one a day, the supply covers 30 full days. The last full day is Tuesday, March 31, 2026 and the first day without a dose is Wednesday, April 1, 2026. With 7 days needed to refill, the reorder date is Wednesday, March 25, 2026.
With 60 tablets and two a day, the supply also lasts 30 days, and a 5 day lead time gives a reorder date of Friday, March 27, 2026. With 15 tablets taken every other day (0.5 a day) the supply lasts 30 days as well.
What this page does
It counts doses and dates. It does not know what medicine you take, how it should be taken, or whether a supply is enough for any purpose. Follow the label and the advice of your prescriber and pharmacist, and do not change how you take medicine because of a date on this page.
It helps to include the day you start in the count, since the first dose is usually taken that day. If you already took today’s dose, enter tomorrow as the first day.
Planning ahead
Allow extra time for weekends, holidays and mail. Many people order a refill a week before the run-out date. To keep track of each dose, print the Medication Schedule, and to count down to your reorder date, use the Countdown Timer to Date. To check the arithmetic by hand, add days with the Date Calculator.
Assumptions and limits
- Doses are taken at an even rate every day, starting on the first day.
- Extra doses, missed doses and changes in the plan are not tracked.
- The count is for information only and is not advice about any medicine.
- Dates use the calendar and ignore time zones.
- The doses, daily doses, dates and lead time shown when the page opens are examples.
Frequently asked questions
Is this medical advice?
No. It only does arithmetic on the numbers you enter. For anything about how or when to take a medicine, ask your prescriber or pharmacist.
What does first day short of a dose mean?
It is the first day on which you would not have a full day of doses left. It is the day after the last full day the supply covers.
What if I take a different number of doses on different days?
Use an average, or run the page once for each stretch of days with a different pattern. The page assumes one steady rate.
Can the reorder date be before my first day?
Yes, if your lead time is longer than the supply. The page still shows the date so you can see you are already late to reorder.