I had posted my thoughts on the Pope's possible plan to retire/resign in August some months ago. I hope that I am not the source of this rumor. From CNS:
Some people think the pope has in mind a one-way trip to his homeland. Under this scenario, he would announce his resignation in his former diocese of Krakow and retire to a Polish monastery to pray. In August, the number of voting members of the College of Cardinals coincidentally falls to 120 -- the upper limit set by conclave rules.
There's not much on the announced papal calendar after August, with the exception of a possible trip to Croatia in September. Vatican officials, aware of the resignation talk, recently emphasized that the Croatia trip was indeed in preparation.