Live in US lawfully without a visa? How 6 months caculated?

so it's 6 months per visit not per 12 months or per calendar year? does anyone know this for an absolute fact? I understand that it is still up to the CBP officer to deny me at any time for any reason but I want to make sure that if I exit in December after my 180 days whether I can return before Jan 1st (or even after Jan 1st if it's per calendar year).

It's six months per visit, unless the CBP officer informs you otherwise, and issues you an I-94 with a shorter date.

But, for undocumented (no I-94 issued) entry into US on B-2 status, you can stay for 6 months from date of entry.

Cdns get confused on this because of the way Provinces calculate healthcare eligibility, which is 183 days in province in any rolling 365-day period (152 for ontario). Most snowbirds adhere religiously to this 'rule' -- never staying outside canada for more than 183 days a year, and thus many people thing that it is one imposed by CBP, but its actually the provincial helthcare driving this.