Weather & Accessibility
EBC is at a very high altitude (17,600 feet/5380 meters), and the overland route to get there is also high. This means that it's never really 'warm' in the Everest region, but there are still dramatic differences in temperature, precipitation, and snowfall throughout the year.
Spring and Autumn
The most popular months for trekking in the Everest region are March, April, May, October and November, as these months are when the conditions are at their best. The spring and the autumn tend to offer reasonable temperatures, clear skies, little-to-no rain, and less chance of problematic snowfall. These months are also when the trails are busiest, but if you're seeking the best weather conditions, that's a trade-off you may be prepared to make.
Winter
The winter (December, January, and February) isn't necessarily a 'bad' time to trek to EBC, but it's certainly the off-season. Temperatures can get extremely cold, so you'd need to be well prepared for freezing conditions. But, the skies tend to be very clear in winter, meaning excellent mountain views. And, you won't be jostling for space with other trekkers en route.
Monsoon
The monsoon season (June to early September) is not an ideal time to travel to EBC. Aside from the wet weather—which can lead to landslides on trails and muddy conditions—rainclouds can obscure the mountain views. But, temperatures are also warmer at this time, and it rarely rains all day every day. If you're well prepared for the rain and don't mind getting a bit wet along the way though, trekking in the monsoon can be fine because the higher you go in altitude, the less rain there tends to be.
If trekking isn't on your agenda but a helicopter tour to EBC is, these are also best when the weather is clear and predictable. That is, any time but during the monsoon.
The weather won't only effect your experience in the Everest region, it also has the potential to affect flights from Kathmandu to Lukla. Flying is the most popular way of getting to Lukla, but flights are frequently canceled when the weather and visibility is poor in Kathmandu, Lukla, or en route. Flights outside of the monsoon season are more likely to run as scheduled, but rain, fog, or smog can effect flights at any time of year. Read more about this flight in the following article: How to Get from Kathmandu to Lukla.
High Season Crowds & Alternate Routes
Spring and autumn are the peak seasons in Nepal, and as the EBC trek is Nepal's most popular, trails can get crowded at these times. There's no chance you'll have the main trails to yourself, and you may also struggle to get your first pick of accommodation. Trekking with a guide is always a good idea, but even more so in the peak season as they will be able to secure beds for you that might be difficult if you were traveling independently. Additionally, the Everest climbing season runs from May to early June, so even if you have no intention of climbing the mountain yourself, the area will be busy with expeditions in these months.
Flights to Lukla also sell out quite far in advance during peak season, so book these as early as possible.
In the winter and monsoon, you won't encounter the same crowds. But while you may not struggle to get a bed in a good teahouse as you might in peak season, a lot of places close in the off-seasons.
The classic EBC trail is the most popular, but there are also many other treks in the region that don't see the same volume of visitors, even in the peak season. Some of these go to EBC via a different route, while others bypass it but still give trekkers a wonderful glimpse into the landscapes, nature, and culture of the Everest region. See the next section for more details.
As already mentioned, the classic EBC trek is best done in spring or autumn for the best weather conditions, but these months bring the issue of overcrowding. To avoid this, check out one of these alternative journeys in the Everest region instead.
The trekking trail from Jiri to Lukla is an alternative to flying to Lukla from Kathmandu, and allows you to enjoy some quiet trails before joining the busy-ness of the Khumbu Valley. It's called the "Pioneers' Route" because it was the trail that early Western mountaineers took to access the Everest region before the airport was built at Lukla. Jiri is a day's drive from Kathmandu. Similarly, fly from Kathmandu to Phaplu and trek through the Solukhumbu region from there. These treks take 4-7 days, and are best done in the peak seasons, as well as winter.
The Gokyo Lakes Trek is one of the more popular alternatives to EBC, but it still doesn't see the same number of visitors. The Gokyo Lakes are the highest freshwater lake system in the world. This trek takes you to the summit of Gokyo Ri, which is around the same altitude as EBC, and has spectacular views of Everest and friends. Another benefit is that fewer nights are spent at high altitude than on the EBC trek. This trek is best done in the peak seasons, when the conditions are best.
The Three Passes Trek is one of the most challenging teahouse treks in Nepal, but is a good option for experienced trekkers who want to avoid EBC's crowds while still enjoying some of the area's highlights. It's a circuit rather than an in-and-out trek, so every day brings something new. Plus, as the name suggests, you'll have the challenge of crossing three high passes. This trek isn't advisable in winter, as the passes are likely to be snow-bound.
The Arun Valley and Everest Base Camp Trek approaches the region from a different direction. It traverses the Arun Valley, which is between the Sagarmatha and Makalu-Barun National Parks. It follows some of the classic EBC route, but diverges enough to keep things interesting. Even in the peak seasons this trail will be practically empty until you reach the EBC trail.
If traveling in winter, consider treating yourself to a luxury tour—there are some lovely luxury lodges in the Everest region on a par with comfortable boutique accommodations in Kathmandu. While this kind of trip is special at any time of year, it's even more so in winter, when you'll especially enjoy the comfort of a warm, cozy lodge at the end of a day of walking. Check out this Luxury Everest Heli Trek itinerary.
Experienced mountain climbers who don't want to tackle Everest but are still up for a challenge should consider climbing Island Peak, a 'trekking peak'. The best time to attempt this is in the peak trekking seasons—spring and autumn—as Island Peak isn't nearly as high (or as risky) as Everest, so has a longer climbing window. The trek there follows much of the same route as the standard EBC trek, and gets you to Kala Patthar, from where there are views of EBC.
Festivals
A highlight of traveling in Nepal is witnessing one of the many vibrant Hindu or Buddhist festivals put on throughout the year. The people of the Everest region are mostly Tibetan Buddhist Sherpas, so have quite a distinct culture to the predominantly Hindu culture of Kathmandu and other hill areas. One of the most important festivals for the Sherpa people is Mani Rimdu, which falls in either October or November. It's worth trying to be in Tengboche for the festival if you can. Tengboche Monastery is the most important monastery in the area, and monks dress in colorful and elaborate costumes to perform ritual dances.
More Useful Information
Best of the Everest Region
How to Get to Everest Base Camp
Unique Ways to Experience Everest Base Camp