Belize gives you the best of both worlds with the second-biggest barrier reef on earth right off the coast and ancient Maya ruins hidden deep in the mainland jungle. If you want to dodge the heaviest crowds and score better rates on beachfront resorts, you need to aim for the shoulder season months of November or April. The weather is still warm, the Caribbean water is clear for diving, and you won't be tripping over tour groups at Xunantunich.
A typical trip runs around $2900 depending on where you stay and which excursions you book. Dropping that much cash at once hurts, so we need a plan to spread it out over time without getting hit with extra fees.
That intro window is a firm deadline, not free money, so make sure you treat it like one. If you still have a remaining balance when those 15 months run out, standard interest charges will kick in on what you owe.