Antibiotic Course Completion Calculator

This calculator tracks where you are in a prescribed antibiotic course: how many doses and days are left, what percentage you have completed, and which day the last dose falls on.

“Always finish the course” needs a caveat now

That slogan has been standard advice for decades, and the reasoning behind it was partly wrong. The old argument was that stopping early lets survivors develop resistance. For most common infections it is the opposite: resistance is driven by how long bacteria are exposed to the drug, so unnecessarily long courses select for it rather than preventing it. A 2017 BMJ analysis made the case publicly, and the evidence for shorter courses has strengthened since.

What has genuinely changed is the length of the prescription, not your freedom to stop. Many infections that once got 10 or 14 days are now treated in 5 or 7. What has not changed:

• Take exactly what you were prescribed. The length you were given already reflects current practice.
• Do not stop early on your own because you feel better. Feeling better happens well before the infection is cleared, and for some infections, including strep throat, endocarditis, tuberculosis and bone infections, stopping early genuinely causes relapse.
• Do call the prescriber if you get side effects, a rash, or no improvement after 48 to 72 hours. That is a reason to change the plan, not to abandon it silently.
• Never save leftovers or share them. If you have leftovers at the end of a correctly taken course, something was miscounted.

How the Calculation Works

The formula is straightforward:

• Total doses = doses per day × total days
• Doses taken = doses per day × days already taken
• Doses remaining = total doses − doses taken
• Days remaining = doses remaining ÷ doses per day
• Completion % = (doses taken ÷ total doses) × 100

Common Antibiotic Courses

Most antibiotic prescriptions run 5 to 14 days:

• 3–5 days: UTI treatments (e.g., nitrofurantoin, trimethoprim)
• 7 days: Strep throat, ear infections, many common infections
• 10–14 days: More complex infections, Lyme disease, pneumonia
• Long-term (months): Acne treatment with low-dose antibiotics

Dosing Schedules

• Once daily (1×/day): Take at the same time each day
• Twice daily (2×/day): Every 12 hours
• Three times daily (3×/day): Every 8 hours
• Four times daily (4×/day): Every 6 hours

Tips for Completing Your Course

Set a phone alarm for every dose, one alarm per dose rather than one a day. Take it with food if it upsets your stomach, unless the label says otherwise, and note that a few antibiotics genuinely must be taken on an empty stomach. Store as directed, since some liquid formulations need refrigerating and go off quickly once made up. Never share antibiotics or keep them for next time.

If you miss a dose

Take it as soon as you remember, unless the next one is nearly due, in which case skip the missed one and carry on. Do not double up. If you have missed several, ring the pharmacy rather than guessing, because whether the course needs extending depends on the drug and the infection.