Probably is an understatement. He's been earning on average more than $40m per year for the past 5 years alone according to the Forbes estimates...
Their estimate from July 2011 to July 2012 was $54.3m.
Federer's previous Forbes estimates were 2011: $47m, 2010: $43m, 2009: $33m... (Sports Illustrated estimated 2010 quite differently, saying it was more like $62m).
Given these sort of numbers, how they're often on the low side and the likelihood he's invested wisely (Credit Suisse might be part of that equation since he's a major part of their marketing) Federer would be worth $250m minimum imo. Considering the sponsorships he has and his longevity I'd be surprised if it was lower - and it could be a lot higher too.