Query the number of days a patent's term has been extended by the USPTO using the ANA_EXT_DAYS field code.  The ANA_EXT_DAYS holds the number of days the patent term has been extended due to 35 U.S.C. 154(b).

It is often useful to search using a range query.

For Example:

ANA_EXT_DAYS:[366 to *]  -->  Returns patents with term extensions longer that one year (366 days or greater).

Some users also want to see patents that have no term extensions.  You can use the FIELD field code to look for patents with no term extensions.

For Example:

FIELD:isEmptyANA_EXT_DAYS -->  Returns patents with no term extension.