The Swiss veteran has taken the last two months off after what he described as a surprisingly successful start to the year that resulted in victory at the Australian Open and then the Indian Wells-Miami Masters double.
"I was terribly surprised to win the Australian Open and to back it up and win the sunshine double in Indian Wells and Miami was a complete surprise to me," Federer said.
Although 35, he has been in fine form during his limited activity this year, losing only once -- a shock reverse to Russian Evgeny Donskoy, then ranked 116, in Dubai.
And while his own resurgence this year has taken him aback, Federer insists that Rafael Nadal's return to claycourt dominance was not so unexpected.
"I think Rafa winning the French Open is less of a surprise because he'd done it nine times before," he said.
"I was hoping he was going to dominate the claycourt season like the olden days."
Having only played in four tournaments this year as he manages his workload, Federer said he would return to a full programme for the rest of the season.
"There are no more breaks now," he told the ATP website.
"I've had enough breaks. I'm a practice world champion now and that's not who I want to be.
"I want to be a champ on the match courts. So I'm going to be playing a regular schedule for the second part of the season."
Federer begins his Stuttgart campaign against German veteran Tommy Haas, where victory would be the 1,100th of his professional career.