I took my 3rd cruise last year. This one was totally free.
I use the carnival card for everything. Took me 3 years, paid for the entire cruise , shuttle, airplane tickets, and some stateroom deliveries.
when I got back, I redeemed the points from my purchases on the cruise for 90 days after, and it paid on some excursions and bar tabs that were eligible.
Now I start over accumulating the points.
I’m guaranteed a cruise every 3 years with this method, and I’ve paid zero interest.
If you spend more then I do, you’ll get your free cruise sooner.
Zero annual fee