What is the latest you can cancel a cruise and get a refund?

This is going to vary depending on if you bought travel insurance or not. If you have paid in full you most likely will end up losing some money. I would call them directly and see what their cancellation policy is. You are going to get to many different answers on that unless a Carnival Employee answers on here for you. I work for Holland and our policy is the following.

Bookings without Insurance -
Cancel before final payment date no penalty
Cancel After final it is anywhere from deposit amount to 100%. The closer to the sailing the more you lose.

With insurance -
No refund on insurance amount, but you can cancel up to 24 hours prior to sailing and get 80-90% refund.

Most cruise lines will allow you to cancel w/o penalties up to your final payment date. Carnivals cancellation policy is…

depending on the length of the cruise

2-5 days 61 days or more before sailing (none)
2-5 days 60-30 days before sailing(deposit amount)
2-5 days 29-8 days before sailing (50% of enitre fare)
2-5 days 7 days or less before sailing (100% penalty)

6-8 days 71 days or more before sailing (none)
6-8 days 70-30 days before sailing (deposit)
6-8 days 29-8 days before sailing (50% of enitre fare)
6-8 days 7 days or less before sailing (100% penalty)