How do I know that an end mill has come to the end of

How do I know that an end mill has come to the end of its life and I need to replace it?
I didn’t find any good answer googling for it…

Generally you can see the cut quality drop in the material and hear your spindle/router working harder. For me burn marks is time to get a new one. Also look with a magnifying glass at the edge and you will see small chips on the edge.

Ok thank you!!!