After your bond reaches original maturity, it automatically enters one or
more extension periods (usually ten years long). During extensions, bonds
issued prior to May 1995 earn interest based on a guaranteed yield or a
market-based yield. The applicable guaranteed yield is the one in effect at
the time the bond enters the extension. Bonds issued after April 1995 have no
guaranteed minimum yield. They'll earn interest in accordance with the terms
and conditions in effect at the time they enter the extension.