Belize runs on a dry-season clock, and the sweet spot is November through April. The rains back off, the reefs are calm enough for snorkeling, and the cayes feel like the Caribbean without the crowds. A week on the mainland or split between the cayes and the jungle tends to land around $520 per person if you keep it simple — local guesthouses, chicken buses, and tacos that cost less than a smoothie back home.
Most people cover a trip like this in one of three ways: cash, debit, or a card that gives them a runway. The third one is only worth it if you can clear the balance before the clock runs out, because what looks like free time is really just deferred interest.
The 18 months is a deadline, not a discount. If the $520 is still sitting on the balance when month 18 lands, the card's standard rate kicks in on whatever is left. Pay it off early and it cost you nothing extra. Leave a balance and it becomes one of the more expensive $520 trips you've ever taken.