Chances are, you have at least one unused gift card laying around somewhere. And if you’re being honest—or if you search hard enough—you probably have two, three or more.

Some 51 percent of U.S. adults currently have unused gift cards, vouchers or store credits, according to a Bankrate.com survey conducted last summer. The average value is $116 per person, and the grand total is more than $15 billion. Most gift cards no longer expire, although they can begin charging inactivity fees after 12 consecutive months of non-use.

Here’s a suggested homework assignment: Round up all of those cards, figure out how much they’re worth and put together a plan to use them. That means emptying the junk drawer, digging into the bottom of your purse and scavenging your sock drawer and glove compartment.

Best ways to use gift cards

You’ll get the best value if you directly use these cards to buy something, whether that’s a treat for yourself or a gift for a friend or family member.

Another option: Many gift cards are reloadable, so you could top off a partially used gift card and give that as a present. In other words, it would be socially awkward to re-gift the remaining $7.87, but if you add $17.13 to make it a more acceptable $25, your recipient is none the wiser, and you essentially saved 31 percent on that gift.

A third option is to sell your unwanted gift cards on a website such as CardCash.com. You won’t get 100 percent of the value if you opt for this route, but it could still make sense under some circumstances (say, if you really need cash now, or if the gift card is for a store that doesn’t fit your personal or gift-giving needs).

How much you’ll receive varies according to the retailer and the payment method you select. It’s often in the 80 percent to 85 percent range. A $100 Target gift card, for example, can be swapped for $82 in cash. A $100 Best Buy gift card is worth $83 and a $100 Pottery Barn card is worth $81.

You can get a bit more than the cash value if you exchange your gift card for a different store-specific gift card. For instance, that $100 Target card is worth $91.02 when it’s converted into a Hotels.com gift card, $87.74 at CVS and $86.10 at The Home Depot (to name a few). Those payouts are 5 percent to 11 percent more than the cash option.

CardCash generally promises quick turnarounds. It pledges to send most payments within a day or two after verifying the gift card balance. It might take another day or two to receive the funds via PayPal or a bank transfer. If you trade your gift card for another store’s card, those are delivered electronically, which shouldn’t take much time. The other option is a paper check—that’s definitely going to take the longest to arrive.

The bottom line

The math points to using gift cards yourself or giving them as gifts. However, getting some value is much better than the nothing you get when your gift cards gather dust.

I’ve sold unwanted gift cards on a few occasions and enjoyed receiving what amounted to free money, even if it wasn’t quite as much as I would have gotten if I had used the cards to buy merchandise.

Have a question about credit cards? E-mail me at ted.rossman@bankrate.com and I’d be happy to help.