For a trademark registration to remain valid, a Declaration of Use must be filed: (1) between the fifth and sixth year following registration and (2) within the year before the end of every 10-year period after the date of registration.
Assuming that a Declaration of Use is timely filed, registrations granted PRIOR to November 16, 1989 have a 20-year term. Registrations granted on or after November 16, 1989 have a 10-year term. Trademarks can be renewed for additional 10-year terms. There is no limit to the number of times a trademark can be renewed, as long as use of the mark by its owner continues.