Sentence examples for days are numbered from inspiring English sources

"days are numbered" is a correct and usable phrase in written English.
It is typically used to imply that something will soon come to an end or reach a conclusion. It can also suggest that time is limited or running out. Example: "The company's days are numbered if they don't increase their sales soon." This suggests that if the company does not improve its sales, it will eventually fail and come to an end.