A trademark can last forever, so long as it remains in use.

Trademark registration deadlines in the US. Trademark registrations issued in the US, other than US extensions of trademarks registered via the Madrid Protocol (which have slightly different deadlines), have several post-registration deadlines:

• Section 8 deadline to demonstrate continued use or excusable non-use. Due between the 5th and 6th anniversaries of the registration date. If the mark has been in continuous and substantially exclusive use for five years, and there have been no adverse decisions about the registrant’s rights in the mark, the registrant can file a Section 15 declaration to make the registration “incontestable” and gain certain additional offensive benefits in a dispute related to that mark. (The registration gains additional defensive benefits just from passing the 5 year mark from registration.)
• Section 8 & 9 deadline to renew the trademark registration and to demonstrate continued use of excusable non-use. Due between the 9th and 10th anniversaries of the registration date, and each 10 years thereafter.

Trademark registration deadlines internationally. Most foreign jurisdictions also have 10-year registration terms, but not all. Some jurisdictions count their renewal deadlines from registration and others count from the application date; be sure to check with local counsel or another trusted resource to be certain.