When do you need to replace your windshield wipers?

What are the signs generally, that indicate that your wipers need to be replaced?When do you need to replace your windshield wipers?
I always buy myself a birthdy present...New wipersWhen do you need to replace your windshield wipers?
Streaking, chattering, basically not doing their job. It's a good idea to replace them before the rainy season anyway. It's easier to find the correct size before the rain starts.
when your winshield doesnt come clean
steakt windows in the rain