My BMs aren’t that regular. Maybe that’s why I get lots of ups and downs.
I weigh daily. I used to weigh monthly, but it was too easy to blame the number on “daily fluctuation,” not enough sleep, or something I ate yesterday. . . . Instead of “Well you’ve been off the wagon for 6 weeks, what do you expect?” So one month I’m up a few pounds, then the next month a few more, and before you know it I’ve gained 20 pounds. If I weigh daily, at least I’m taking a daily interest in what’s going on, and can decide what (if anything) to do about it.
As has been said here, the choice depends on a number of personal factors.
At the beginning I was driving myself crazy and focusing on just the numbers, so my cousin, who got me started on the Keto Train, took my scale and had it in the trunk of her car. We got together once a month to do measurements and then “Norman” would come out from the trunk. This time away from my scale obsession allowed me to focus on my NSVs and pay attention to my body signals.