I think most people weigh in whenever they feel the need

Some do it every day, others once a week, some every two weeks.

If you do it daily, avg out the highs and lows for the week. Daily weigh ins will flux 2-4 pounds depending on time of day and water drank etc.

For instance the other morning I weighed 155, yesterday I woke up and weighed 159, this morning I was back to 155.5. *shrugs*

Scales are interesting in the jokes they play.