How long is the flu contagious?
Last updated September 3, 2026.
You can spread the flu from about 1 day before symptoms start until 5 to 7 days after you get sick - and you are most contagious in the first 3 days. That pre-symptom day is why flu tears through households: people spread it before they feel sick. Young children and people with weakened immune systems can shed virus for longer. Flu travels mainly through droplets from coughs, sneezes, and conversation, and through surfaces you touch and then your face. A sound return-to-work rule is 24 hours fever-free without fever-reducing medicine, plus extra care around high-risk people for a few more days. If you are unsure whether you have flu or a cold, Pymander is a free AI doctor, 24/7 by text, and can help you sort the difference.
What to do
- Isolate hardest in the first 3 days: that is your peak contagious window.
- Wait for 24 hours fever-free without medicine: not just feeling better - actually fever-free.
- Protect high-risk people longer: older adults, pregnant people, and the immunocompromised deserve a wider berth.
- Ask about antivirals early: they work best within 48 hours of symptoms starting.
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