Flu or COVID? How to Tell Them Apart

Flu and COVID-19 can look almost identical at first. You might have a fever, cough, sore throat, body aches, fatigue, or a stuffy nose with either infection. That makes it difficult to know what you have based on symptoms alone.

There are some patterns that can offer clues. Flu often comes on more suddenly, while COVID-19 may take longer to show up after an exposure. Loss or change of taste or smell is more associated with COVID-19, though it isn't a reliable way to diagnose it. Testing is the only way to confirm which virus is causing your symptoms.

Here's what to know about flu vs COVID symptoms, home testing, contagiousness, and when it makes sense to get medical care.

TL;DR: Key Takeaways

• Flu and COVID-19 share many of the same symptoms, including fever, cough, fatigue, body aches, headache, sore throat, and congestion.
• Flu often starts more suddenly, while COVID-19 can take longer to cause symptoms after infection.
• Loss or change of taste or smell is more commonly associated with COVID-19, but it can't confirm that you have COVID.
• A home COVID test can be useful, but one negative antigen test doesn't completely rule out infection.
• If you have COVID symptoms and your first home antigen test is negative, the FDA recommends repeating the test 48 hours later.
• Flu is usually contagious starting about one day before symptoms and for about five to seven days after becoming sick. People are generally most contagious during the first three days.
• Both flu and COVID can cause serious illness, particularly in people at higher risk of complications.
• Antiviral treatment for flu and COVID works best when started early, so people at higher risk should contact a healthcare professional promptly if they develop symptoms.

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Flu vs COVID symptoms: How do they compare?

The biggest problem with comparing flu and COVID is that there's so much overlap. Both infections can cause respiratory symptoms and whole-body symptoms.

This is why there's no reliable symptom checklist that can tell you "This is definitely flu" or "This is definitely COVID." Testing is needed to confirm the infection.

Does flu usually start differently from COVID?

Sometimes.

Flu symptoms often appear relatively suddenly. A person may feel fine and then develop fever, chills, body aches, headache, cough, and fatigue within a short period.

COVID-19 can also start suddenly, but the time between infection and symptoms can be longer. The CDC says flu symptoms typically appear about one to four days after infection, while COVID-19 symptoms can appear about two to five days after infection and, in some cases, up to 14 days later.

That difference can be useful when thinking about a recent exposure, but it still can't tell you which virus you have.

Flu vs cold symptoms: How can you tell?

A cold is another possibility when you have a cough, congestion, sore throat, or runny nose.

In general, flu vs cold symptoms tend to differ in intensity. Flu usually causes more intense symptoms and often begins more abruptly. Colds are generally milder and are more likely to cause a runny or stuffy nose, sneezing, and a sore throat.

Fever and significant body aches are more suggestive of flu than an ordinary cold, but there's enough overlap that symptoms alone still can't provide a definite diagnosis.

If you have cold-like symptoms and there's a possibility of flu or COVID, testing can be particularly useful if you're at higher risk for complications because treatments for both infections work best when started early.

Is a home COVID test still accurate?

Yes, but a negative result doesn't always rule out COVID-19.

Most at-home COVID tests are antigen tests. They're convenient and provide results quickly, but they're less sensitive than molecular tests, particularly early in an infection. That means you can have COVID and still receive a negative result on an early rapid test.

What should you do after a negative home test?

If you have COVID symptoms and your first at-home antigen test is negative, test again 48 hours later. The FDA recommends at least two tests over three days for people with symptoms.

If you don't have symptoms, the FDA recommends testing again 48 hours after the first negative result and again 48 hours after the second negative result, for a total of three tests over five days.

The practical takeaway is simple: one negative rapid test isn't enough to completely rule out COVID, especially early in an infection.

If your tests remain negative but your symptoms continue, a healthcare professional may recommend a laboratory-based molecular test or testing for flu, RSV, or another respiratory virus.

A positive home antigen test, on the other hand, generally means you likely have COVID-19.

Can you have flu and COVID at the same time?

Yes.

It's possible to have influenza and COVID-19 at the same time, though coinfection isn't considered common. Because the symptoms overlap so much, testing can be useful when knowing the specific infection would affect treatment or precautions. Some tests can check for influenza and SARS-CoV-2 at the same time.

Having a positive test for one virus also doesn't automatically mean another infection is impossible. If your symptoms seem unusually severe or continue to worsen, talk with a healthcare professional.

How long is the flu contagious?

How long is the flu contagious? For most people, influenza can spread from about one day before symptoms begin through roughly five to seven days after becoming sick.

People are usually most contagious during the first three days of illness. Young children and people with weakened immune systems may be contagious for longer.

So feeling better doesn't necessarily mean you're no longer able to spread the virus.

If you have flu symptoms, staying home while you're sick, avoiding close contact with others, and taking reasonable steps to reduce respiratory spread can help protect people around you.

How long is COVID contagious?

COVID-19 can also spread before symptoms appear, and some people can spread the virus without having noticeable symptoms. Compared with flu, people with COVID-19 may remain contagious for longer.

Because contagiousness varies between people and depends on the course of the infection, symptoms and timing alone aren't a reliable way to determine whether you're still infectious.

If you test positive for COVID-19, follow current public health guidance and take steps to avoid exposing other people, particularly those at higher risk of severe illness.

When should you get tested for flu?

A flu test can be useful when your symptoms could be caused by several respiratory infections or when knowing whether you have influenza would affect treatment.

There are several types of flu tests. Some rapid tests are less sensitive than other testing methods, so a negative rapid flu test doesn't always rule out influenza. A healthcare professional may also diagnose flu based on your symptoms and the situation in your community, even without a positive test.

If you're at higher risk of complications from flu, don't wait several days for symptoms to become severe before contacting a clinician. Antiviral treatment works best when started early.

When does flu or COVID treatment work best?

Timing matters for both infections.

Flu antivirals are most useful when started early, particularly for people at higher risk of complications. COVID-19 treatments are also time-sensitive and may need to be started within a specific period after symptoms begin.

That's one reason not to spend several days trying to determine whether your symptoms "feel more like flu" or "feel more like COVID." If you're at higher risk for severe illness, contact a healthcare professional promptly after symptoms begin. For more on getting Tamiflu quickly when you're within the treatment window, see our guide on Tamiflu works best within 48 hours.

For people who are otherwise healthy and have mild symptoms, treatment may focus primarily on rest, fluids, and managing symptoms while the infection runs its course.

When should you seek urgent or emergency care?

Most respiratory infections don't require emergency treatment, but some symptoms shouldn't be ignored.

For adults, seek urgent medical attention for symptoms like:

• Difficulty breathing or shortness of breath
• Persistent chest pain or pressure
• New confusion
• Difficulty waking or staying awake
• Severe weakness or unsteadiness
• Severe dehydration or very little urination
• Symptoms that improve and then suddenly become worse
• Any severe or rapidly worsening symptom that concerns you

These warning signs can occur with flu, COVID-19, or other serious respiratory infections.

For a child, emergency warning signs can be different, so parents should seek medical care for severe breathing problems, dehydration, unusual sleepiness or lack of responsiveness, seizures, or other concerning symptoms. If you're not sure whether you need urgent care or emergency care, see our guide on urgent care vs ER: how to decide in 60 seconds.

Conclusion

Flu and COVID-19 have too many symptoms in common to reliably distinguish them by how you feel alone. Fever, cough, fatigue, body aches, congestion, headache, and sore throat can happen with either infection.

Flu may come on more abruptly, while COVID-19 can take longer to cause symptoms after infection. Loss or change of taste or smell is more associated with COVID-19, but it isn't enough to diagnose it.

If you're wondering whether a home COVID test is still accurate, the answer is yes, but a single negative rapid test doesn't completely rule out infection. If you have symptoms and test negative, repeat the test 48 hours later.

And if you're wondering how long the flu is contagious, remember that people can spread flu about one day before symptoms begin and for around five to seven days afterward, with the highest contagiousness generally occurring during the first three days.

When the diagnosis matters, testing is more useful than trying to match your symptoms to a checklist. And if you're at higher risk for complications, getting medical advice early can matter because flu and COVID treatments work best when started promptly.