Google PageRank Update Schedule for the year 2011:

First 2011 PageRank (PR) Update

Time-frame: 31 January - 3 February

Second 2011 PageRank (PR) Update

Time-frame: 30 June - 3 July 2011

Third 2011 PageRank (PR) Update

Time-frame: 30 September - 3 October 2011

Fourth 2011 PageRank (PR) Update

Time-frame: 31 December - 3 January 2012

All these updates are major PR updates.

The data is the assumption based on previous PR updates.

Google Generally updates website or blog PageRank PR 4 times in a year.