The short answer is that Costa Rica is great year-round. The longer answer is that the two seasons offer genuinely different trips, and which suits you depends less on the calendar than on what you want from the visit.
Dry season and green season
Dry season runs November to April. This is the classic window, and the better bet for outdoor activities — hiking, ziplines, beaches and anything where you would rather not plan around rain.
Green season runs May to November. The trade-off is straightforward: more rain, but lush landscapes, fewer crowds, and lower prices.
How the seasons change what you do
The activities run year-round, but the season shapes the experience.
In dry season, the full range of outdoor activity is comfortably available, and full-day commitments like whitewater rafting or a combined waterfall-and-volcano day are easier to plan with confidence.
In green season, the forest is at its most alive. Cloud forest is at its most atmospheric when there is actual cloud in it, and waterfalls are at their fullest. Wildlife tours that run at the edges of the day are largely unaffected by afternoon rain, since they are scheduled outside the wettest part of the day anyway. Farm tours and hot springs are effectively weather-proof.
One note for Tortuguero: sea turtle nesting there is seasonal. If that is the reason for your trip, confirm the timing before building an itinerary around it.
How long to stay
We recommend 7 to 10 days for Costa Rica's highlights, with a minimum of 3 nights in each major destination.
That minimum is about travel time as much as anything. Destinations here are separated by three- to four-hour drives, and mountain roads, unpaved stretches and — in Tortuguero's case — a boat connection mean arrival days are genuinely travel days.
Entry requirements
Most visitors from North America, Europe and many other countries do not need a visa for stays of up to 90 days. Requirements change, so check with your local Costa Rican embassy for your specific situation before you travel.
So, when should you go?
If your priority is reliable weather for a packed outdoor itinerary, aim for the dry season. If it is lower prices, fewer people and landscapes at their greenest, the green season rewards you for the flexibility.