Does your parents health insurance cut you off automatically when you get married or is there a period?

Once you marry, you're automatically not eligible any more. It can take the insurance company up to eight weeks to process it in the computer, or find out about it through your parents, HOWEVER, when it gets processed/discovered, the cancellation goes retroactively back to the day of the marriage.

You WILL eventually get billed in full, for those services.

Your parents fill out paperwork once a year for their health insurance. When they last filled it out, you were single (and probably living with them or a student) so you qualified to be covered under their policy.

Mom and Dad are supposed to notify the insurance company of your change in status as soon as it happens during the period in between that once a year paperwork filing. If no one notifies the insurance company of a status change, chances are they will never find out and process the bill. Next year at paperwork time Mom and Dad then don't put your name down and everyone goes on with their life.

Of course if you gave the hospital your new married name, flags will probably go up at the insurance company. After all, they have you under one name and not the other and that's something they check on all claims as a matter of routine.

(20 year claims veteran with the scars to prove it)

It does not cut you off because you turn 18. It used to cut you off at 19 unless you were a full time student. A few policies can still do that, but most now have to wait until you are 26. It can cut you off at any time, for other reasons, but not because you turned 18.

Usually cuts off on the date of marriage.

When all else fails, read the policy!