Gronkowski's agent, Drew Rosenhaus, announced the revised deal via social media, posting congratulatory posts to his client on Twitter and Instagram.
Per ESPN and the NFL Network, Gronkowski can receive a maximum of $13.3 million in 2018 that will include up to $4.3 million in additional incentives.
Gronkowski, who is signed through the 2019 season, will receive $1 million in game bonuses and can earn three additional $1.1 million performance incentives.
The Patriots worked out a similar deal with quarterback Tom Brady earlier this month, adding $5 million in incentives to the three-time NFL MVP's salary for 2018.
The 6-foot-6, 265-pound Gronkowski posted 69 catches for 1,084 yards with eight touchdowns over 14 games last season.
A second-round draft pick of the Patriots in 2010, Gronkowski has been a touchdown machine since joining the team, reaching double digits in five of his eight seasons, including a career-high 17 in 2011.
Gronkowski has surpassed 1,000 yards four times and has 474 receptions for 7,179 yards in 102 career games (89 starts).