“Take for 10 days” sounds like it ends ten days after you start. It often does not, because the first day is rarely a full day of doses. Count the doses rather than the days, and the last one can land on day 11.
Course end date
A course → date of the last dose
The course
Nothing you type here leaves your browser.
Count doses, not days
A 10-day course at three a day is 30 doses. If the first dose was at 3pm and only two fit into that day, the 30th lands on the morning of day 11. Pharmacists generally mean “finish the doses you were given”, which is why this tool counts the doses and lets the last day fall where it falls.
Every so many hours
For an “every 8 hours” label, the last dose is the first one plus 8 hours for each dose after it. If the clocks change during the course, the time shown keeps the real gap, so it will be an hour off your usual clock time for the rest of the course.
If you miss a dose
Whether to take it late, skip it or add it to the end depends on the medication. The leaflet usually says; if it does not, ask a pharmacist. This tool assumes every dose is taken on schedule.
To tick off each dose as you go, print the course on the dosing calendar. For the clock times of an “every N hours” schedule, use the dose interval calculator, and the antibiotic reminder write-up covers keeping a short course on track.
Common questions
When does a 10-day course end?
Count doses rather than days. A 10-day course at 3 a day is 30 doses. If you took all 3 on the first day, the last dose is on day 10. If you only took 2 on the first day, the 30th dose falls on day 11.
How long do 21 tablets last at 3 a day?
7 days, if you take all 3 on the first day. The last tablet is taken on day 7.
When is my last dose if I take it every 8 hours for 7 days?
7 days every 8 hours is 21 doses. The last dose is 20 gaps of 8 hours, or 160 hours, after the first. A first dose at 08:00 on day 1 puts the last one at 00:00 at the very start of day 8, which is midnight at the end of day 7.
One thing this cannot do
This is an arithmetic tool, not medical advice. It works out numbers from what you type in — it does not know your medication, your prescription, or what you should do if something goes wrong. Anything about changing a dose, spacing doses differently, or handling a missed dose is a question for your doctor or pharmacist.