The U.S. Treasury Department reports that billions of dollars in matured but unredeemed U.S. savings bonds remain in circulation. These Series EE and I savings bonds stop accruing interest 30 years after their issue date. According to IRS regulations, deferred bond interest is taxable in the year the bond matures, not when it is redeemed, which could lead to unexpected tax bills for unaware heirs. Currently, matured bonds generate no yield, while the 10-year U.S. government bond yield stands at 4.79% (as of September 2), meaning purchasing power is eroded with each month of delay.