What is expiration date normaly of doxycycline,100mg?

With doxycycline, discard it a year after it was filled. This is one medication that goes bad with age, and can actually harm you. You shouldn't have any around anyway, since you're supposed to take them all when prescribed.

It's difficult to say what the expiry date on doxycycline pills would be. It depends on what brand, etc. it is. If it was dispensed lately then the pharmacy that dispensed it may be able to give an approximate time as to which date it would expire.

If it was dispensed a while ago then it would be very difficult to say when it would expire.