Source: Tom Brady got $16M bonus

The four-year contract extension signed by New England Patriots quarterback Tom Brady includes a $16 million signing bonus, according to a source.

As part of the extension, Brady had his base salary in 2010 increased to $7.5 million. He had been scheduled to earn a base salary of $3.5 million this season, and had previously earned a $3 million roster bonus.

Brady will earn base salaries of $5.75 million in 2011; $5.75 million in 2012; $9.75 million in 2013; and $9.75 million in 2014.

The $5.75 million base salary in 2011 is guaranteed.

Meanwhile, Brady has roster bonuses of $4 million in 2011, $6 million in 2012, $5 million in 2013 and $5 million in 2014.

He can also earn $250,000 workout bonuses in 2011, 2012, 2013 and 2014, adding another possible $1 million to the pact.

While initial reports pegged the total guarantees in the deal at $48.5 million, the details of the contract add important context. Brady could earn $49.5 million in guarantees and bonuses as part of the deal, but $21 million in roster and workout bonuses aren't guaranteed in the event of a career-ending injury this year.

Mike Reiss covers the Patriots for ESPN Boston. You can follow him on Twitter.