People with COVID-19 are generally contagious from about 1 to 2 days before symptoms begin and remain contagious for up to 8 to 10 days after symptom onset

. The highest contagiousness tends to occur early in the illness, particularly around the day symptoms start and the first few days thereafter

. For most individuals with mild to moderate symptoms, contagiousness typically lasts around 8 days, but it can vary depending on factors such as the severity of illness and underlying health conditions

. Some people, especially those who are severely ill or immunocompromised, may remain contagious for longer periods, potentially up to 20 days

. People can also spread the virus even if they do not have symptoms (asymptomatic spread), which complicates control measures

. After about 5 days from symptom onset, contagiousness usually decreases, but precautions such as masking and physical distancing are still recommended for several days afterward to reduce transmission risk

. In summary:

• Contagious period starts ~1-2 days before symptoms.
• Most contagious in the first 5 days of symptoms.
• Contagious for about 8-10 days after symptoms begin for most people.
• Can be longer (up to 20 days) in severe or immunocompromised cases.
• Asymptomatic individuals can also spread the virus.
• CDC guidelines allow ending isolation after 5 days if fever-free for 24 hours and symptoms improve, but continued precautions are advised.

This timeline aligns with guidance from the CDC, NHS, Yale experts, and other health authorities