You're probably sitting on at least $167 of unused gift cards

More than $20 billion in unredeemed gift cards and store credit is floating around the U.S. and there is a good chance some of it belongs to you, according to a survey commissioned by Bankrate.com.

Half of all U.S. adults have about $167 in some form of unused credit, including airline redemption vouchers, the survey found. People with household income over $80,000 have the most in unused credit, at $297, followed by those with minor children ($274), and millennials ($234).

If those numbers seem high to you, consider that Starbucks alone reported $1.7 billion in store value card liability — accounting speak for unredeemed gift cards — as of Dec. 31. Shoppers bought $425 million of the coffee company's cards in the fourth quarter. Meanwhile, the retailer Target had $683 million in gift-card liability as of Nov. 2.

Almost as startling is that one-quarter of U.S. adults have allowed a gift card to expire. Ted Rossman, an analyst at Bankrate.com, says that's totally unnecessary.

“Gift cards and store credits are real money,” Rossman said in a phone interview. “The longer you hold it, the more likely you are to lose it. Or the company could go bankrupt.”

Unwanted gift cards can be sold in a robust secondary market on sites such as Cardpool.com, CardCash.com and GiftCardSpread.com. And there's also always the tried-and-true regifting option.

“The best thing you can do is buy something for yourself or someone else,” Rossman said.

The survey of 2,602 adults was conducted Jan. 15-17 by YouGov.

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Bloomberg's Alex Tanzi contributed to this report.