How Long Is the COVID-19 Incubation Period?

Medically Reviewed by Zilpah Sheikh, MD on January 07, 2024
Written by Sonya Collins, Evan Starkman
6 min read

The incubation period is the number of days it takes for symptoms to appear after you’re infected with something. Health care professionals and government officials use this number to decide how long people need to stay away from others during an outbreak. It’s different for every condition.

If you’ve been around someone who has the coronavirus that causes COVID-19, you’re at risk, too. That means you need to stay home until you know you’re in the clear. Health professionals call this self-quarantine. But when will you know you're sick? The answer depends on the COVID-19 incubation period.

Viruses are constantly changing, which sometimes leads to new strains called “variants.” Different COVID-19 variants can have different incubation periods.

When researchers set out to learn the incubation period for the original strain of COVID-19, they studied dozens of confirmed cases reported between Jan. 4 and Feb. 24, 2020. These cases included only people who knew that they’d been around someone who was sick.

On average, symptoms showed up in the newly infected person about 5.6 days after contact. Rarely, symptoms appeared as soon as 2 days after exposure. Most people with symptoms had them by day 12. And most of the other ill people were sick by day 14. In rare cases, symptoms can show up after 14 days. Researchers think this happens with about 1 out of every 100 people.

Some people may have COVID-19 and never show symptoms. Others may not know that they have it because their symptoms are very mild. Current studies might not include the mildest cases, and the COVID-19 incubation period could be different for these.

How long after exposure will you test positive for COVID-19?

Depending on which COVID-19 variant you've been exposed to, you may test positive 3-5 days later. If you've been exposed to the virus but don't have any symptoms, wait for 5 days before you get tested. If you test too early and you do have COVID-19, you may falsely test negative.

The Omicron variant, which evolved from previous strains of COVID-19, was once the most dominant type of coronavirus in the U.S. Research shows it spreads faster and has a shorter incubation period than the SARS-CoV-2 variants that came before it.

Omicron’s incubation is around 3 days, compared with 4-5 days for earlier strains. This means that if you get infected with the Delta strain, your symptoms may show up much faster. Your body will also shed the virus (meaning you're contagious) earlier.

The mutation allows the virus to produce a higher load of viral particles in the body. This makes the Omicron variant more than two times as contagious as earlier variants.

Vaccines and booster shots help protect people from serious illness, hospitalization, and death. If you’re fully vaccinated and you get a breakthrough infection of Omicron, you’re less likely to become seriously ill than an unvaccinated person.

Researchers estimate that people who get infected with COVID-19 can spread it to others 2-3 days before symptoms start and are most contagious 1-2 days before they feel sick.

if you have the Omicron variant, you may become contagious more quickly because of its shorter COVID-19 incubation period. But we need more research on this.

According to the CDC, if you have mild to moderate COVID-19, you may be contagious for 10 days from the first day you notice symptoms.

If you were severely affected or critically ill from COVID-19, you may stay infectious for up to 20 days from the start of your symptoms.

Your infectiousness is highest 1 day before the start of your symptoms and begins to wane about a week later for most people.

The Omicron variant has a shorter COVID-19 incubation period compared with other variants. For the Omicron variant, the incubation period is 1-4 days.

When you get a COVID-19 vaccine, it teaches your immune system to recognize the virus as a foreign element and fight it. Studies show that COVID-19 vaccines can greatly reduce your chances of getting infected with the virus. But if you do catch it after you’re vaccinated, the vaccine will still help protect you from getting as seriously ill or needing hospitalization.

It’s important to note that you’re not optimally protected until 2 weeks after you get your second dose of a two-shot vaccine. That’s because it takes around 2 weeks for your body to build protection against the virus. And because the incubation period is shorter than the wait time between doses, it’s possible to catch COVID-19 before or just after your vaccination, as your body has not had enough time to build immunity. If this happens, the CDC recommends waiting until you’ve fully recovered to get the vaccine.

The CDC says that if you might have come into contact with the virus and have no symptoms, you should self-monitor. This means watching for signs such as fever, cough, and shortness of breath. Stay out of crowded places, keep at least 6 feet away from other people, and wear a high-quality face mask when you have to go out.

If you know that you came into contact with someone who has COVID-19, you should self-quarantine if you are:

  • Fully vaccinated with possible COVID-19 symptoms
  • Unvaccinated or not fully vaccinated

If you’re unvaccinated or are more than 6 months away from your full vaccination and haven’t yet had your booster shot, the CDC recommends you:

  • Isolate for 5 days.
  • Follow strict mask use for 5 more days.

But if the 5-day quarantine isn’t possible for you, the CDC suggests you wear a well-fitted mask around other people for 10 days after exposure.

If you’ve gotten your vaccination and booster shot, you don’t need to quarantine after coming into contact with a positive COVID-19 case. But you should wear a mask for 10 days after exposure.

If you’ve been exposed in any case, the best option would also include a COVID-19 test on the fifth day after exposure. If you start to have symptoms, you should quarantine until you get a negative test that shows your symptoms weren’t caused by COVID-19.

Still, after you leave quarantine, you should continue to monitor yourself for any symptoms.

Take extra safety measures if you think or know you have COVID-19, or if you test positive for the virus but don't have symptoms. Isolate yourself from other people in your home. Choose a “sick room” or a separate area to stay in, and use a different bathroom if possible.

The CDC has shortened its recommended isolation time for people with COVID-19 who don't have symptoms to 5 days. After this period, they suggest you wear a mask around others for 5 more days.

If you have been exposed to someone with COVID-19, you may begin to show symptoms after a 3-5 day incubation period. The amount of time will depend on the variant you were exposed to. Staying up to date on COVID-19 booster vaccinations will lower your chances of becoming seriously ill with the virus.

  • How long does it take for symptoms of COVID-19 to appear after exposure?

    COVID-19 symptoms may show 2-14 days after you've been exposed to the virus. This timeline depends on which variant you were exposed to.

  • What is the most common incubation period for COVID-19?

    The incubation period varies for different strains of COVID-19. On average, the incubation period for COVID-19 across all variants is about 6 days.