On March 19, 2013, the USPTO's new fees became effective. The most notable changes were the maintenance fees due at three intervals: 3½, 7½ and 11½ years after patent issuance. At each interval, the fees increase with the new top-fee set at $7,400 -- a 50% increase over the old fee.
With the major fee increase, it is no surprise that savvy patent owners took advantage of the opportunity of paying the renewal fees early. The USPTO allows patentees to pay the fees due up to six-months early or, with a $160 fee, up to six months late.