Gift cards make great stocking stuffers—just as long as you don't stuff them in a drawer and forget about them after the holidays. Americans are expected to spend nearly $30 billion on gift cards this holiday season, according to the National Retail Federation. Restaurant gift cards are the most popular, reports the AP, making up one-third of those sales. Most of those gift cards will be redeemed. Paytronix, which tracks restaurant gift card sales, says around 70% of gift cards are used within six months. But many cards—tens of billions of dollars' worth—wind up forgotten or otherwise unused. That's when the life of a gift card gets more complicated, with expiration dates or inactivity fees that can vary by state. Here's what to know about the gift cards you're giving—or getting: