Peak Season: November–April. The coastal weather is heavenly, with temperatures of 80°F and near-constant ocean breezes. Rates reflect increased demand from sun-starved northerners, especially in Playa del Carmen. During Christmas week, hoteliers tack on as much as $200 a night—so if you're planning a Christmas vacation, you'd do well to book six months in advance.

Off Season: June, September, and October. September and October bring the worst weather, with frequent rain, mosquitoes, and the risk of hurricanes. There's also often rain in June. Breezes disappear, and humidity soars, especially inland. But if you're looking for a spa getaway and don't mind the weather outside, hotel rates can drop on the Caribbean Coast by as much as 50% in the low season.

Sweet Spot: May, July, and August. Low-season prices and sunny skies make late spring and midsummer a great time to save on airfares and hotels, while having beaches to yourself.