Millions of Americans aren’t playing their cards right.

In fact, we’ve left more than $44 billion on the table, in the form of unused gift cards, according to a new study.

“People are letting cash slip away that they could be using,” says John Kiernan, a senior analyst with CardHub. Kiernan, citing CardHub numbers, estimates that some $44 billion in unredeemed gift-card value has been accumulating since 2008.

“I’m not surprised by that number at all,” adds Bill Hardekopf, CEO of LowCards. “People get these cards and often put them away in a drawer and then forget about them. And that’s too bad.”

Gift cards have become a popular way to do holiday shopping; 80 percent of shoppers expected to buy a gift card this past holiday season, spending more than $118 billion in all.

Consumers on average were expected to spend $163 each on gift cards. That’s up about 4 percent from the previous year, according to the National Retail Federation.

For retailers, however, gift-card sales don’t count as revenue until cards are used, meaning that retailers are holding $44 billion in liabilities against these unused cards.

So the largest seller of gift cards, Walmart, has come up with a plan to persuade its customers to use this deferred gift.

Walmart is telling shoppers to spend the cards on add-ons for gaming systems they buy or on accessories for smartphones and tablets that they may have received for Christmas.

Yet these cards represent more than just a chance to buy a gift at some department store. Consumers, thanks to market forces and new laws, now have more options, say credit-card industry experts.

For example, today there are several gift-card exchanges that will pay cash for unused cards. Generally, Hardekopf says, consumers can expect to get 80 to 85 cents on the dollar in exchange for the gift card.

CardHub offers one such exchange, as does GiftCardRescue and CardPool. Another factor is now working in favor of consumers: The danger of these gift cards expiring is now much less. CardHub’s Kiernan notes that the value of these gift cards is now good for five years.

“People should put this money to productive use,” Kiernan adds, cautioning that some people who do redeem gift cards will use all their value and then add more to a purchase, which puts them deeper in credit-card debt.

Hardekopf adds that consumers with unused gift cards should research the fees in using them. “Some cards charge fees, such as a monthly fee, after 12 months of inactivity,” he says.