Expresses that something will soon come to an end. Often hints at inevitability and lack of control. With the new regulations, it seems that the old factory's days are numbered.
Pro Tip 2/3
Negative Tone
The phrase usually carries a negative sentiment and often implies failure or death. After the scandal, the politician's days were numbered.
Pro Tip 3/3
Slight Formality
Somewhat formal, used more in written language or serious discussions rather than casual conversation. The report suggests that these species' days are numbered due to climate change.