Flu Contagious Period. Flu starts being contagious about 24 hours before you have symptoms. You're most contagious when you first get sick and for the following 2 to 3 days. The severity of your symptoms correlates to how many new viruses are being produced, so you're less contagious as you start to feel better. Most people stop being infectious approximately 5 to 7 days after getting sick, but you can remain contagious for as long as 10 days. Limiting Flu Spread To limit the spread of flu, the Centers for Disease Control and Prevention recommends staying home while you're sick and for at least 24 hours after your fever breaks.