Anyone who does not opt for a day one test on arrival at the airport will have to self-isolate for the full 21 days.
Those who do take a test on arrival and are offered a day 13 test will be free to go out into the community on or around day 14 if their test comes back negative.
At a meeting on Monday [11 Jan], the Civil Contingencies Authority considered the increasing prevalence rates of Covid-19 in neighbouring areas, transmission rates of the new variants and the new measures around essential travel only into the Bailiwick.
Day-of-arrival testing, along with a day 13 test carried out at the drive-through testing centre at the PEH, is now essential in order for passengers to secure an isolation exit on or around day 14.
Children under 12 will only need a negative test on day 13.
If travellers are self-isolating in a bubble with family or friends, all non-travellers will also need a negative day 13 test to qualify from 'early release' from the mandatory 21 days of self-isolation.
There is no change for critical workers coming to the Bailiwick. They will still need to comply with their specific self-isolation and testing requirements.
Director of Public Health Dr Nicola Brink said this method means positive travellers will be picked up on arrival, as well as those presenting late infections at day 13.
'The day one test is also beneficial for track and trace purposes should this be needed,' she said.
'Asking people to have both tests in order to leave self-isolation on day 14 rather than day 21 protects the Bailiwick as we continue to fight this pandemic.'
Chair of the CCA Deputy Peter Ferbrache said at the media briefing on Friday 8 January that measures have been put in place to ban all but essential travel into the Bailiwick.
'Those who much travel for critical or essential reasons need to work with us to protect the Bailiwick from Covid-19.
'Asking travellers to have a negative day one and day 13 test result is a belt and braces approach to pick up early and late presenting infections,' he said.