You can have a "master calendar" that has all of your board's due dates, either within Trello or by linking your boards to an external calendar like Google.
Within Trello, you can enable the Planyway Calendar Power Up. See more about that here http://info.trello.com/power-ups/planyway-calendar (This is the method I recommend, as it's real-time reporting on the calendars for all boards and it's kept within Trello)
For linking to an external calendar, there are a few ways to accomplish this
1) Using the iCal feed: http://help.trello.com/article/811-viewing-cards-in-a-calendar-view
2) Use Cronofy for Trello: https://trello.cronofy.com (I recommend this if you're going the route of linking to external calendar)
Cronofy is a bit more reliable, and allows for quicker updates, as iCal feed only updates about once every 24 hours.
Check those out
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