You wouldn’t stash a pile of cash under your mattress, right? But many people are essentially doing just that by not cashing in matured U.S. savings bonds.

According to the Bureau of Public Debt, there are $16 billion worth of savings bonds that have fully matured (meaning they’re no longer earning interest) but have not been cashed in.

Some bondholders don’t cash in because they don’t realize their bonds have matured and assume the bonds are still increasing in value. Others may have forgotten they even own a savings bond—40 million bonds purchased between 1941 and 1978 have never been redeemed. The Treasury does not send out notices to bondholders when their bonds have matured.

How can you find out if you have unclaimed savings bond money waiting for you?

To check the status of Series E savings bonds purchased in 1974 or later:

• If you know the bond’s serial number, you can easily find out if it has matured by visiting the U.S. Treasury’s online savings bond calculator.
• If you think you own a bond but don’t know the serial number, you can plug your Social Security number into the site’s Treasury Hunt tool to find information on any unredeemed bonds.

For bonds purchased before 1974:

• You’ll need to write to the Bureau of Public Debt’s record-keeping office: Bureau of the Public Debt, P.O. Box 7012, Parkersburg, WV 26106-7012
• Provide the name or names on the bond, the address at time of purchase, the approximate issue date and denomination of the bond, and any other information that might be helpful in tracking the bond down.
• If a record of the bond is found, the bureau will let you know how to cash in the bond.

For bonds owned by deceased relatives:

• They can still be cashed in by their heirs.
• Follow the same steps above for bonds issued before or after 1974, using the information of the deceased bondholder.

Paper savings bonds can be redeemed at almost all local financial institutions. Electronic bonds can be purchased, managed and redeemed on the Treasury Direct website.

Elizabeth Nolan Brown is a Web content manager for AARP Bulletin Today.