You are usually contagious with the flu from about 1 day before symptoms start until about 5–7 days after they begin, with the highest risk in the first 3–4 days of feeling sick. Children, older adults, and people with weakened immune systems can shed the virus and stay contagious for longer than a week.

Key timing at a glance

  • Before symptoms: Flu virus can be detected and spread about 24 hours before you feel sick, so you can be contagious even when you feel normal.
  • Most contagious window: The first 3–4 days after symptoms (fever, aches, cough) start is when you are most contagious.
  • How long it lasts: Most adults remain contagious for about 5–7 days after symptom onset, even if they start to feel better earlier.
  • Longer in some people: Young children and people with weak immune systems may stay contagious beyond 7 days.

Practical stay-home guidelines

  • Stay home and avoid close contact with others until:
    • It has been at least 24 hours with no fever (without fever-reducing medicine), and
* You feel clearly improved and are coughing/sneezing less.
  • If you still have frequent coughing or sneezing after 5–7 days, be extra careful around high‑risk people (babies, pregnant people, elderly, those with chronic illness).

How flu spreads most easily

  • Flu mainly spreads through droplets when an infected person coughs, sneezes, or talks at close range.
  • It can also spread by touching contaminated surfaces and then touching your nose, mouth, or eyes.

Simple ways to protect others

  • Wear a mask around other people during the first few days of illness if you must go out.
  • Cover coughs/sneezes, wash hands often, and avoid sharing cups, utensils, or towels.
  • Annual flu vaccination reduces your risk of getting sick and helps cut down how much virus you might spread if you do get infected.

If you’re unsure whether it’s flu

  • Flu often comes on suddenly with fever, body aches, fatigue, and dry cough, but other infections (like colds or COVID‑19) can look similar and have different contagious periods.
  • Testing or professional medical advice is especially important if you’re high‑risk or feel very unwell.