The cancellation policy for a cruise varies by line and you must understand what you are agreeing to when you make a booking. Always ask your agent what the terms are, or check the cruise line conditions online or in their brochure.
You will usually find deposits are non-refundable and only sometimes are even transferrable to an alternative cruise if you change your mind. A name change on a booking is often also counted as a cancellation and significant fees can apply.
You usually have to pay the full balance of a fare 90 days before a cruise, and in full if booking within this timeframe. Some lines stagger the cancellation charges the closer to the departure date while others will keep it at the full fare after paying this balance.
As deposits are usually lost if you cancel your cruise before the 90 days and full fare if after this time frame, you should consider taking out travel insurance at the time of booking to cover you incase you need to change your plans. The terms can be very strict and even illness will still see you loosing your deposit or fare if you have to cancel. So insurance is the best way to cover yourself against this eventuality.
When making a booking do not let the excitement of the idea of cruising cloud you making sound financial decisions to cover yourself against lost.