Bathroom rug replacement

zachdecker thought this was worth mentioning said
1

I am cheap. I don’t like to buy new things when an old one is still somewhat adequately serving its purpose. But at what point is a bathroom rug just disgusting and needs to be replaced?

I don’t consider myself to be an adequate judge of this, so I need input.
Does a bathroom rug need to be replaced after 6 months? Each year? 2 years? 5?
I really have no idea.