Log in to your Target account, then click "Gift cards" to see the remaining balances of your gift cards.
You can verify your balance on your card by calling 800-544-2943 from your phone. You will be asked to confirm the balance of your card.
https://targetegiftcardbalance.com/
https://sites.google.com/targetgiftscardredeem.com/targetgiftcardbalance/