How often do dogs come into season?

A female's first season is usually before she is a year old. Thereafter she usually has a season every 6-7 months unless pregnant or spayed.

If you do not have a purebred, registered dog with titles and ancestors with titles, please spay her. There is no need for BYB (back yard bred) dogs which are only slightly better off than puppy mill dogs. Additionally, it is very unpleasant living with a female in season. She gets cranky and or airheaded. She leaves blood drops all over. She smells. She attracts stray dogs. It's just plain best to avoid the whole mess.