The pendency is the amount of time between the file date of a patent and the grant date.  To query patents by their pendency use the ANA_PEND field code.

For un-granted applications the pendency is the number of days that have elapsed since the patent was filed.  Once an application "grants" the pendency remains fixed.  AcclaimIP re-computes the pendency field every week.

Pendency is an important value indicator with a unique value profile.  The median pendency is 1126 days or about 3.1 years.  As pendency increases, the average length of claim one (the first independent claim) also increases.  This suggests that a long pendency narrows the patent as the applicant responds to rejections from the patent office.  If you've prosecuted patents, then you will not find this surprising.

However, as pendency gets very long, it is an indicator of interference proceedings, and is often NOT indicative of rejections and further narrowing of the scope of the claims.  Therefore, patents with very, very long pendencies tend to be some of the most valuable patents.

In the figure below, the ANA_PEND field measures the Pendency Gap.