Are these farewells formal?

Question

Are these farewells formal?

A dopo
A tra poco
A presto
A domani

Answer 1

The forms of salutations you cite are very common and colloquial. They are typically used with friends and people you are familiar with. They are similar to the more internationally known forms such as:

ciao

and

arrivederci.

A few of the above forms are defined by De Mauro Dictionary

1) A dopo , 2) A più tardi, 3) A presto