Everyday. Fleet of work vehicles checked as part of daily checklist in addition to other items. My personal vehicle when I'm at the office weekly by my shop or if I'm not around my office before and during every long driving trip at least monthly as part of my regular routine.
Truck is every 1000 miles or so, usually down about 1/2 qt by that time. Top it off and check in another 1000.
Wife's Santa Fe, Was checking every fill up for the first year we had it, never down any, so now only about 1/2 way through the OCI (~2,500 miles).
Scion is checked every few fill ups. Never needed topping off, but has been about 1/2 qt low at time of oil change.
Mom's Kia, whenever I see her, every few weeks usually. Has never been low in the past year.
Motorcycle, only just before and just after changing the oil. In the 2500 mile OCI it has never gone down, so not worried about it.
Sisters vehicles, when I get a chance, usually every 2 months or so, usually adding a qt to both of them.
On the newer cars probably monthly but maybe sooner.
On my oil burner that the teenagers use, definitely every two weeks or less. It also gives me peace of mind to poke around on the kids' car so that I have a higher likelihood of finding things that need attention sooner rather than later.
If it is a vehicle known to leak or burn oil , every time I fill up with fuel . Otherwise , every oil change .
Last 20 years , on the company truck I drive , never . I take it to a quick change oil place , they change oil / filter & the boss gets the bill .
In my youth , engines both leaked and / or burned oil , to a much greater extent than they do now . On average .
May not be the best method , but it works for me .
Every couple of days. OCD, because my car doesn't burn much. Soul owners forums (especially Facebook sites) are full of people (who usually name their cars--that should tell you something) who never check their oil and pay for it. My daughter trashed a nice Geo Prizm by running it down to nothing, then when I chided her, putting in a full quart on every gas fill up. Think she had about nine quarts in their-- last use of STP kept it going for a while. Doesn't take much time to pull that dipstick.
You know those Geo Prizms had a rather good durable motor in them if I am remembering that correctly. .
Kind of like the Chevrolet Cavalier... Those cars also had a really decent motor in them too if they were taken care of well.
Beins my Truck uses no oil, I only check it after I take it somewhere to have it changed. One time I think I didn't get a new oil filter as the oil with 10 miles was less than clean.
In Oil Level Checks We Trust. Not the oil change guy.