It takes five days on average for people to start showing the symptoms of coronavirus, scientists have confirmed.
The Covid-19 disease, which can cause a fever, cough and breathing problems, is spreading around the world and has already affected more than 114 000 people.
The US team analysed known cases from China and other countries to understand more about the disease.
Most people who develop symptoms do so on or around day five.
Anyone who is symptom-free by day 12 is unlikely to get symptoms, but they may still be infectious carriers.
The researchers advise people who could be infectious - whether they have symptoms or not - to self-isolate for 14 days to avoid spreading it to others.
If they follow that guidance - which has already been adopted in the UK and US - it is estimated that for every 100 individuals quarantined for a fortnight, one of them might develop symptoms after being released, Annals of Internal Medicine reports.