(one's) number is up American British phrase
used to say that someone is about to suffer, die or be punished.
You never know when your number's up, so just live the best life that you can!
OMG, I just broke my mom's favorite vase, my number's up.
When the ship started to sink, Ken thought that his number was up.
Luana: I got F for my final exam, my number is up. Liza: Learn by experience and study hard next time. Everything will be fine.
There is 'to be' in the phrase, therefore it needs to conjugate within the sentence. Besides, we should use this phrase in the appropriate context.
Used when something unpleasant has happened that has spoilt what you intended to do
Oh, no, that’s torn it! I’ve left my wallet at home!