Amoxicillin Dose Calculator
An amoxicillin dose calculator for adults shows the standard dose, frequency, and course length for common infections, drawn from the FDA-approved dosing table. Unlike pediatric dosing, adult dosing is fixed, not weight-based: mild to moderate ear, nose, throat, skin, and urinary infections take 500 mg every 12 hours or 250 mg every 8 hours, while severe infections and lower respiratory tract infections take 875 mg every 12 hours or 500 mg every 8 hours. Select your infection and severity below.
Children under 40 kg are dosed by weight, not with these fixed doses: use our amoxicillin pediatric dosing calculator for weight-based mg/kg/day regimens with milliliter conversions.
Standard adult dose, frequency, and course length by infection
Educational estimate from the FDA dosing table. Follow the prescription label exactly; confirm any uncertainty with the prescriber or pharmacist.
Quick Answer
💡 Key takeaways
- Adult dosing is fixed, not weight-based: 500 mg q12h (or 250 mg q8h) mild/moderate; 875 mg q12h (or 500 mg q8h) severe.
- Lower respiratory infections always use the higher dose, whatever the severity.
- Strep throat needs 10 days minimum to prevent acute rheumatic fever, even after symptoms resolve.
- Continue 48-72 hours beyond symptom resolution; the daily ceiling is 4,000 mg.
The FDA dosing table, explained
The FDA label organizes adult dosing by infection site and severity in one table. Ear, nose, throat, skin, and urinary infections share the same bands: mild/moderate = 500 mg every 12 hours or 250 mg every 8 hours, severe = 875 mg every 12 hours or 500 mg every 8 hours. Lower respiratory tract infections skip the lower band entirely and use the severe dosing at any severity. Gonorrhea is the outlier: a single 3-gram dose.
The two frequency options are equivalent by design: 500 mg twice daily and 250 mg three times daily both deliver 1,000-1,500 mg per day within the effective range. Twice daily wins on adherence, which is why it is the default in the tool.
| Infection | Twice daily (q12h) | Three times daily (q8h) | Duration |
|---|---|---|---|
| ENT / skin / urinary, mild-moderate | 500 mg | 250 mg | 7-10 days |
| ENT / skin / urinary, severe | 875 mg | 500 mg | 7-10 days Higher dose |
| Lower respiratory tract | 875 mg | 500 mg | 7-10 days |
| Strep throat | 500 mg (875 if severe) | 250 mg (500 if severe) | 10 days minimum |
| Dental infection | 500 mg every 8 hours | 7-10 days | |
Worked example: sinus infection, 500 mg twice daily
An adult with a mild to moderate sinus infection selects ear/nose/throat, mild/moderate severity, twice daily, 7 days. The tool returns: 500 mg per dose, every 12 hours, 1,000 mg per day, and 7,000 mg for the whole course. These are the tool’s exact outputs for these inputs.
If the same infection were judged severe, the dose becomes 875 mg every 12 hours (1,750 mg/day, 17,500 mg over 10 days), still well under the 4,000 mg daily ceiling. The calculator shows the schedule and the course total so you can see the full prescription at a glance.
Duration rules: the 10-day strep requirement
Most courses run 7-10 days, and treatment should continue at least 48-72 hours beyond symptom improvement or confirmed bacterial clearance. Strep throat is stricter: the FDA label requires a minimum of 10 days for any Streptococcus pyogenes infection to prevent acute rheumatic fever, and the tool enforces this automatically when strep throat is selected.
- Start on schedule. Take doses evenly spaced; food is optional but can reduce stomach upset.
- Keep going past feeling better. Symptoms often resolve days before the bacteria are cleared.
- Hit the strep 10-day mark. Non-negotiable for streptococcal infections, whatever the calendar says.
- Do not save leftovers. Unfinished antibiotics must not be reused later or shared.
- Call if it worsens. No improvement after 48-72 hours, or any allergic signs, needs the prescriber.
Twice daily vs three times daily: does it matter?
Clinically, both schedules work when the dose is adjusted to match: the label pairs 500 mg twice daily with 250 mg three times daily for the same indication. The difference is practical. Twice-daily dosing fits meals and sleep and is measurably easier to complete; three-times-daily keeps blood levels steadier through the day, which some prescribers prefer for tougher infections.
The common failure is not the schedule but the improvisation: doubling a missed dose, or switching schedules mid-course without guidance. Pick the schedule on the prescription and keep it.
What competing calculators miss
Most amoxicillin dose tools are pediatric-only or give one flat “500 mg three times daily” answer for every adult infection, which contradicts the label’s severity bands and site-specific dosing. Others never mention the 10-day strep rule or the 48-72 hour continuation rule, the two duration details that actually protect patients. Few show the course total, so users cannot sanity-check the prescription quantity.
This calculator implements the full FDA table (site × severity × frequency), enforces the strep 10-day minimum automatically, flags the 4,000 mg daily ceiling, and shows daily and course totals. It stays in its lane, though: it is an educational reference, not a prescription, and it says so plainly.
Frequently Asked Questions
500 mg every 12 hours or 250 mg every 8 hours for mild to moderate infections; 875 mg every 12 hours or 500 mg every 8 hours for severe infections and lower respiratory tract infections. The daily ceiling is 4,000 mg.
Usually 7-10 days, continuing 48-72 hours beyond symptom resolution. Strep throat requires a minimum of 10 days to prevent acute rheumatic fever.
No. Stopping early lets the infection return and contributes to antibiotic resistance. Complete the full prescribed course even after symptoms resolve.
4,000 mg per day for adults. Standard regimens stay well under this; the calculator flags anything above it.
It can be taken with or without food. Taking it with a meal may reduce stomach upset, which is the most common side effect.
Mild nausea or diarrhea is common. Hives, facial swelling, or difficulty breathing signal possible allergy and need immediate medical care; severe or bloody diarrhea also warrants a call to the prescriber.
References
- U.S. Food and Drug Administration / DailyMed. Amoxicillin capsules: dosage and administration (FDA label). Accessed October 19, 2026.
- National Library of Medicine / MedlinePlus. Amoxicillin: MedlinePlus Drug Information. Accessed October 19, 2026.
- Centers for Disease Control and Prevention. About Antibiotic Use. Accessed October 19, 2026.
- DrOracle. Typical Amoxicillin Dosage and Treatment Duration for Bacterial Infections. Accessed October 19, 2026.
- DrOracle. Recommended Amoxicillin Dosage for Mild to Moderate Infections. Accessed October 19, 2026.
- DrOracle. Effective Amoxicillin Dose for Acute Otitis Media and Streptococcal Pharyngitis. Accessed October 19, 2026.
- CanadaPharmac. Amoxicillin Typical Dosage by Infection. Accessed October 19, 2026.
- Mountainside Medical. Amoxicillin Uses and Dosage Information. Accessed October 19, 2026.
- NursingCalc. Pediatric Drug Dosage Calculator: mg/kg for Children. Accessed October 19, 2026.
- MDApp. Amoxicillin Pediatric Dose Calculator: Indication-Based Dosing. Accessed October 19, 2026.