Cozumel's calendar has a clear shape. High season runs from about the middle of December through April, and the island prices accordingly. September is the cheapest and quietest month of the year, with October close behind. May, June and November sit in between.
What moves, and by roughly how much
Treat all of this as direction rather than arithmetic, because operators set their own rates and the peso moves.
- Accommodation shows the largest swing. Expect high-season rates well above the low-season equivalent for the same room, with the sharpest spikes around Christmas, New Year, Easter week and Carnaval.
- Diving moves less than hotels do. Shops adjust seasonally but the gap between a February two-tank and a September one is modest. Where you save in low season is availability: you can book the day before.
- Beach club day passes are relatively stable, because they are priced against cruise volume rather than the hotel calendar.
- Taxi fares do not move with the season. They are set by zone and passenger count, and the tariff is posted.
- Flights and ferries follow the usual holiday-demand pattern rather than anything local.
What crowding actually means here
The variable that matters most is how many ships are in port, and that peaks with the same December-to-April window.
On a four-ship morning: the taxi rank at Puerta Maya moves slowly between about nine and ten, the moorings at Palancar stack up with catamarans by midday, the beach clubs fill, and San Miguel's malecón is a shopping street. On a one-ship day in September, the same island is quiet by ten in the morning.
If your dates are flexible and you are not tied to school holidays, a shoulder-season week — May, early June, or November — gives you close to high-season conditions with meaningfully fewer people.
The catch with September
A number of small dive shops, restaurants and east-coast bars take their annual maintenance closure in September. It is also the peak of hurricane risk and the second-wettest month.
None of that makes it a bad month. It makes it a month that requires confirming, individually, that the specific operator, restaurant or bar you are planning around is actually open. Do that by message rather than by looking at a website, which on this island is frequently out of date.