If you only have four fingers...

It depends on which one I'm missing.

Depends on which finger is missing. Each fingers keep their names, regardless of if all five of them are on your hand.

I have 4 fingers and 1 thumb, so index, middle, ring and pinky
JK
EDIT: probably index, middle and pinky

the pinky is smaller than the other fingers, so I'm inclined to say that.
Additionally, those hands usually wear their wedding rings on the third finger, not the last one.

View attached image.

Alice, Jill, Lisa, Michelle, Gertrude.

Rosie's five sisters.

Thank you all, I'm gonna go with the pinky!