Antibiotics kill bacteria within hours, but you typically feel better in 2 to 3 days, because symptoms lag behind the kill.
The rough map by infection: strep and UTIs ease within 48 to 72 hours, ear infections about the same, sinus and skin infections several days to a week. The order of improvement: fever breaks first, then pain and energy, then the signature symptoms fade last. Two rules outrank the timeline: finish the entire course even when you feel cured (the survivors of an early stop are the hardier bacteria, which is how resistance and recurrence happen), and treat day 3 with zero improvement, or improvement then sudden worsening, as a call-the-doctor checkpoint, since that pattern means the drug or the diagnosis is wrong. One calibration: most sore throats, coughs, and sinus congestion are viral, so no antibiotic timeline applies; that is why watchful waiting is often the right prescription.
What to do
Common questions
How long do antibiotics take to work?
Antibiotics start killing bacteria within hours of the first dose, but feeling better takes longer because symptoms lag behind the bacterial kill: the NHS guidance for amoxicillin, representative of most antibiotics, is that you should feel better within a few days for most infections. The typical pattern by infection: strep throat and UTIs usually ease within 48 to 72 hours, ear infections similar, sinus infections and bronchitis-type bacterial infections 3 to 5 days, and skin infections a few days to a week. What "working" actually looks like day by day: fever breaks first, then pain and energy improve, then the specific symptoms (discharge, cough, urinary burning) fade last. Two rules that matter more than the timeline. First, finish the entire course even when you feel cured by day 3, because the surviving bacteria are the hardier ones, and stopping early breeds resistance and recurrence. Second, the call-the-doctor checkpoint: no improvement at all by day 3 on antibiotics, or improvement followed by a sharp worsening, means the diagnosis or the drug is wrong, resistant bacteria, a viral infection mislabeled, or an abscess that needs draining. And a calibration note: most sore throats, most coughs, and most sinus congestion are viral, and no antibiotic timeline applies to them, which is why "wait and see" is often the correct prescription.