DCL deposit is 20% of the total cruise cost.
As of March 3, 2015, when the balance is due and what the cancellation policy is varies by the length of the cruise and what type of room you have (concierge vs non-concierge usually). It used to be a standard 75 days.
Cancellation policies tend to be steeper than WDW, for example, once you are in the final payment window, most likely you'd completely lose at least the 20% deposit unless you are cancelling for a reason covered by insurance and you have the insurance.