Is this a card for AT&T prepaid wireless service? There's no way to check the card short of attempting to apply it to your service. If it hasn't been used, the balance should still be on the card. After the amount is added to your account, it can expire. $10 to $24 expires in 30 days. $25 to $99 expires in 90 days. $100 and up last 365 days.
Let us know if we can help with anything else.
James, AT&T Community Specialist
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