Does the expiry on a class one medical run to midnight on the date that's on the medical, or midnight of the night before ?
The former (ie midnight [local] on the date shown in the "
expiry date" box on the certificate). You are legal to fly all day on the stated expiry date, if a revalidation medical is not undertaken by then.
However, leaving it to the last minute is not to be recommended for professional pilots. If a desperate rostering department phones you, even on what is supposed to be a day off, "
sorry, my medical has expired" is NOT likely to go down at all well with the company ! !
As
ecj rightly said, you can renew within the 45 days prior to expiry without losing any validity at all. Much more sensible.