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, 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.

After clothing, gift cards will be the most popular present this holiday season. Nearly half of Americans plan to give them, according to the National Retail Federation. But many will remain unspent.

Gift cards get lost or forgotten, or recipients hang on to them for a special occasion. In a July survey, Bankrate found that 47% of U.S. adults had at least one unspent gift card or voucher. The average value of unused gift cards is $187 per person, a total of $23 billion.

While it may take gift cards years to expire, experts say it’s still wise to spend them quickly. Some cards—especially generic cash cards from Visa or MasterCard—will start accruing inactivity fees if they’re not used for a year, which eats away at their value. Inflation also makes cards less valuable over time. And if a retail store closes or goes bankrupt, a gift card could be worthless.

Possible Preaching Angle:

In the same way, the gifts of God (his promises, salvation, spiritual gifts, talents, the Bible) often remain unused, unopened by faith, and neglected by so many people.