Weekly for me! Unless im using the brush every single day then I’ll usually use for half the week, then use a new one for the remainder and wash them all at the end of the week.

I don’t use many brushes, only an eyebrow brush occasionally. I don’t wash the brush nearly anywhere enough.

I like the Ecotools, e.l.f, and Mecca max cleaners. All are effective at removing built up makeup. I don’t wash them as regularly as I like, aiming for monthly.

I’m a bit slack but then being retired and home a lot I don’t use them as often now. Annually with a gentle laundry wash and well rinsed.

I get the makeup brush cleaner from Daiso. Its cheap and it works well.
I am just getting over an eye infection so at the moment I am washing my bushes daily with a set i use and a set that has just been washed ready for the following day.
Normally Its every 3 to 6 weeks depending on how busy I am.