For most healthy people, the flu lasts 3 to 7 days. Fever and body aches tend to clear up within that window, but cough and fatigue often linger for two weeks or longer, especially in older adults and people with chronic lung disease.
The Day-by-Day Timeline
Flu symptoms typically hit fast. Within a few hours you can go from feeling fine to dealing with fever, chills, muscle aches, headache, and exhaustion. A sore throat, runny nose, and cough usually follow. The first three to four days are the worst, and this is also when you’re most contagious.
By days 5 through 7, fever usually breaks and the intense body aches start to fade. You’ll likely still have a cough and feel wiped out, but the sharp, miserable phase is behind you. The cough and a general sense of tiredness can stick around for two weeks or more. That lingering period is normal and doesn’t necessarily mean something has gone wrong.
How Long You’re Contagious
You can spread the flu starting about one day before you even feel sick. That means you may be passing the virus to coworkers, family members, or classmates before you know you have it. After symptoms appear, most healthy adults remain contagious for roughly 5 to 7 days.
Children and people with weakened immune systems can shed the virus for 10 days or longer after symptoms start, and in some cases several weeks. People who carry the virus without showing symptoms can also spread it to others, which is one reason the flu moves through households and schools so quickly. Contagiousness peaks in the first 3 to 4 days of illness and is highest while you still have a fever.
When Kids and Older Adults Take Longer
Children often run higher fevers and may be sick for a longer stretch than healthy adults. Their bodies also shed the virus for a longer period, meaning they’re contagious well past the point where an adult would stop spreading it. Young children are also more likely to develop ear infections or croup on top of the flu itself.
Older adults and people with chronic conditions like asthma, diabetes, or heart disease tend to experience a slower recovery. Cough and fatigue can persist well beyond two weeks in these groups. The risk of the flu progressing to pneumonia or other complications is also significantly higher, which can extend the illness from days into weeks.
Can Antivirals Shorten the Flu?
Prescription antiviral medications can reduce how long the flu lasts, but the benefit depends heavily on timing. Starting treatment within 36 to 48 hours of symptom onset provides the clearest benefit, shortening fever and overall illness duration. The closer to the start of symptoms you begin, the better the results.
Starting treatment later still offers some help. One clinical trial in children found that beginning antiviral treatment even 72 hours after symptoms started reduced illness by about one day compared to no treatment. Antivirals also appear to reduce viral shedding, which means you stop being contagious sooner. Your doctor is most likely to prescribe them if you’re in a high-risk group or if your symptoms are severe.
Post-Flu Fatigue Is Real
Even after the fever, aches, and cough are gone, many people feel drained for days or weeks. This post-viral fatigue is one of the most frustrating parts of the flu because you feel like you should be better, but your energy just isn’t there. For most people, this phase lasts one to three weeks.
In a smaller number of cases, post-viral fatigue can stretch on for several months. Full recovery sometimes takes a year or more for people who develop persistent post-viral fatigue, though this is uncommon after a straightforward flu infection. If you’re still exhausted weeks after your other symptoms cleared, scaling back on exercise and sleep demands rather than pushing through tends to help recovery.
Signs the Flu Has Turned Into Something Else
The typical pattern is that you feel terrible for a few days, then gradually improve. The red flag to watch for is a “second wave,” where you start getting better and then suddenly worsen. A new or worsening fever after day 5, increasing shortness of breath, chest pain, or thick discolored mucus can signal a secondary bacterial infection like pneumonia or bronchitis. These complications require their own treatment and can add weeks to your recovery.
In children, warning signs include rapid or labored breathing, refusal to drink fluids, and severe irritability. In adults, confusion, persistent vomiting, or dizziness when standing up warrants prompt medical attention.
When You Can Go Back to Work or School
The CDC recommends staying home until both of these are true: your symptoms are improving overall, and you’ve gone at least 24 hours without a fever, without using fever-reducing medication like ibuprofen or acetaminophen. That 24-hour clock resets every time your temperature spikes again.
Keep in mind that meeting this threshold doesn’t mean you’re no longer contagious. You may still be shedding virus for a few days after your fever breaks. Washing your hands frequently and covering coughs during that first week back reduces the chance of passing it along to the people around you.