While difficult to predict, generally it's around 18 months out:
"Winter": first cruise in the new year up to April/May (not including spring Panama Canal and Transatlantic) – sometime between late September to early November
"Summer": cruises from about May to August/September (not including fall Panama Canal and Transatlantic) – mid February to early April.
"Fall": September until the end of the year (ending with the last cruise starting in the old year) – generally around May.
GET UP TO A $1000 SHIPBOARD CREDIT AND AN EXCLUSIVE GIFT!
If you make your Disney Cruise Line reservation with Dreams Unlimited Travel you’ll receive these incredible shipboard credits to spend on your cruise!