Traveling from Denmark to USA - when to get Covid Test?

Here is information on the 1-day requirement from the CDC.

The 1-day period is 1 day before the flight’s departure. The Order uses a 1-day time frame instead of 24 hours to provide more flexibility to the air passenger and aircraft operator. By using a 1-day window, test acceptability does not depend on the time of the flight or the time of day that the test sample was taken.

For example, if your flight is at 1pm on a Friday, you could board with a negative test that was taken any time on the prior Thursday.

So it's relative to the day of departure.

Here's the current info from the CDC (Centers for Disease Control) for which tests are valid. Rapid tests are allowed but must meet certain criteria. Information is from this website, "Requirement for Proof of Negative COVID-19 Test or Documentation of Recovery from COVID-19",, accessed 20 December 2021 and excerpted below:

What types of SARS-CoV-2 tests are acceptable under the Order?

You must be tested with a viral test to look for current infection – these include an antigen test or a nucleic acid amplification test (NAAT).

Phrases indicating a test is an antigen test could include, but not are not limited to:

• Rapid antigen test
• Viral antigen test

Also, could be noted as

• Antigen Chromatographic Digital Immunoassay,
• Antigen Chemiluminescence Immunoassay, or
• Antigen Lateral Flow Fluorescence

Examples of available NAATs for SARS-CoV-2 include but are not restricted to:

• Reverse transcription polymerase chain reaction (RT-PCR)
• Isothermal amplification including:
  • Nicking endonuclease amplification reaction (NEAR)
  • Transcription mediated amplification (TMA)
  • Loop-mediated isothermal amplification (LAMP)
  • Helicase-dependent amplification (HDA)
  • Clustered regularly interspaced short palindromic repeats (CRISPR)
  • Strand displacement amplification (SDA)

The test used must be authorized for use by the relevant national authority for the detection of SARS-CoV-2 in the country where the test is administered.

A viral test conducted for U.S. Department of Defense (DOD) personnel, including DOD contractors, dependents, and other U.S. government employees, and tested by a DOD laboratory located in a foreign country also meets the requirements of the Order.

A more direct FAQ, "Can I Get a Rapid Test?", has this answer:

Rapid tests are acceptable if they are a viral test that meet the requirements under the Order.

Self-tests are allowed only if you have an associated tele-health appointment. The medical professional has to confirm that it's you, etc.

It is possible to get tested at Copenhagen airport directly before your flight see Copenhagen Airport testing

PCR tests take 4-6 hours to get results normally, and this is even more complicated over the Christmas period (see the link). However Rapid Antigen tests are reported in 15-30 minutes, will be acceptable to US as they take place under the auspices of the testing company and provide an English certificate.

It is not immediately clear to me if you need to book this in advance or can just turn up, but of course you would want to leave extra time before your flight.