Every time you tap, the Hop reader will display the time/date that your fare expires. You can ride buses and trains until that time. If you tap your card again after that, you’ll be charged another fare. If you tap a card with no balance, you’ll see a red “X” and a “Transaction Denied” message.
You can also check the time remaining and balance on your Hop card at myhopcard.com, using the Hop app or by calling 1-844-MYHOPCARD (694-6722).