Checking my last day of health coverage

I was told my coverage ends on my last day, but the letter says the end of the month. There are 8 people counting on me, so I am trying to be careful. I do not want to be surprised by a bill. Did coverage match what HR said?

Dental and vision sometimes end on a different date from medical. Mine did.

Ask HR to confirm the exact date in writing. I also called the insurance company to double-check.