When Is Marathon Season, Month by Month

42cal's calendar holds 537 marathons, and October and April carry more of them than any other months. Together the two hold a third of the total. The shape reverses by region: Europe and the US peak in spring and autumn, while Asia, the Gulf and the southern hemisphere run largely in the opposite months.

Marathon times slow as heat rises, and slower runners lose more time than fast ones. Ely and three co-authors tracked seven marathons, six in the US plus Vancouver, Canada, over as many as 36 years. The top men slipped from 1.7 percent behind the course record on the coolest quarter of race days to 4.5 percent on the hottest. Their paper stated plainly that "there is a progressive slowing of marathon performance as the WBGT increases from 5 to 25 degrees C." It added that performance suffers more for slower runners than for fast ones. A separate analysis of 1.79 million marathon performances in six major cities put the temperature for fastest running between 3.8 and 9.9 degrees Celsius, the exact figure depending on how fast the runner already is. A third study, of the Stockholm Marathon since 1980, found the same pattern. Moving from 10 degrees to 25 degrees added about 5 minutes for an elite man and 23 for a four-hour man. That paper closed on a note for race organizers: "attention should be paid to the dates and starting times of races."

Why July and August nearly empty out

American College of Sports Medicine guidance tells organizers to schedule events away from whichever months are extremely hot and humid locally, based on historical weather data, and to hold summer events during the cooler hours of the day. Once the wet-bulb globe temperature passes 28 degrees Celsius, the guidance says consideration should be given to canceling or rescheduling a continuous event. The cool Twin Cities Marathon averages under one heat-stroke case per 10,000 finishers. An 11.5-kilometer summer race in the same document averages 10 to 20 per 10,000 entrants. Houston's January mean is 12.1 degrees Celsius against 29.5 in July, and its marathon runs in January.

Twenty-eight marathons still run in July and August, in six groups.

Southern-hemisphere winter (8): Gold Coast, Sunshine Coast and Sydney, Australia; Campinas and Floripa, Brazil; Córdoba, Argentina; Asunción, Paraguay; Victoria Falls, Zimbabwe.
Altitude or mountains (8): the Gornergrat Zermatt Marathon in Switzerland, which draws about 1,200 runners onto a course through the Alps, plus two Bavarian races, Deseret News in Utah, Rapid City in South Dakota, the Guelaguetza Marathon in Oaxaca, the Mexico City Marathon and Guatemala City.
High latitude (7): Helsinki and Turku, Finland; Stavanger, Norway; Aberdeen, Scotland; Edmonton and Nova Scotia, Canada; Hokkaido, Japan.
Evening start (1): Rostock, Germany, beginning at 18:00.
Other US races (3): San Francisco, on a cool coastline, plus Jack & Jill in Washington and Santa Rosa in California.
Outlier (1): Hyderabad, India, at a race-day temperature 42cal estimates near 28 degrees Celsius, in the middle of monsoon season.

Marathon season, month by month

Month	Marathons	Where they cluster	A race that month
January	25	Asia and the US South tied at 7 apiece, four Gulf races and Marrakech close behind at 5	Houston, Hong Kong, Dubai and Mumbai all race on the same day, January 17
February	29	Led by the US, 11 of the 29	Tel Aviv Marathon
March	33	The US ahead at 13, Asia close behind at 8	Tokyo Marathon, an Abbott World Marathon Major
April	78	Europe's biggest spring month at 38, the US next at 25	Boston Marathon and the London Marathon "Double," both Majors
May	67	The US leads at 27, just ahead of Europe's 26, while the southern hemisphere starts waking up at 9	Sanlam Cape Town Marathon, set to become the newest Major
June	32	Spread across the US (11), Europe (9) and Latin America (5)	Jakarta International Marathon
July	14	The US leads narrowly at 5, tied close by Europe and the southern hemisphere at 4 each	Gold Coast Marathon
August	14	Europe, Latin America and the southern hemisphere tied at 4 apiece	TCS Sydney Marathon
September	46	Europe ahead at 21, the US close behind at 19	Berlin Marathon, a Major
October	103	Europe (43) and the US (37) both peak together	Chicago Marathon, a Major
November	62	The US leads at 20, then Europe at 16	New York City Marathon, a Major
December	34	The US leads at 12, with Asia close behind at 11, its busiest month	Valencia Marathon

The regions that run in reverse

Europe and the US follow the spring-and-autumn pattern most closely, since their cool months line up with April and October. Asia, the Gulf and the southern hemisphere don't share that season, so their marathons cluster elsewhere. Hong Kong's climate record puts its January mean at 16.5 degrees Celsius against 28.9 in July. Its 70,000-runner marathon runs in January. Dubai's climate record shows January highs near 24 degrees against 40.6 in July, and its 30,000-runner marathon also sits in January. Mumbai's January mornings run near 17 degrees against 25 in July, cool and dry ahead of the monsoon, and its 60,000-runner marathon follows the same calendar. The US South does the same. All seven of the country's January marathons, Houston's among them, sit in warm-winter states such as Texas, Florida and Louisiana.

Training plans and entry windows, timed to the calendar

Hal Higdon's Novice 1 program runs 18 weeks and peaks with a 20-mile long run three weeks before race day. Higdon's page calls it "arguably, the most popular training program used by first marathoners anywhere." London Marathon Events offers "free 16-week plans" at four levels, one of them for beginners. An 18-week build for an early-October race such as Chicago starts in early-to-mid June and runs through the hottest part of summer. The same build for a late-April race such as London starts in late December and runs through winter instead.

Entry closes on a separate calendar, well ahead of training. Tokyo's general lottery for its March 7, 2027 race closed applications on August 28, 2026, about six months out. Boston's qualifier registration for its April 19, 2027 race runs across mid-September 2026, roughly seven months ahead. Chicago's lottery for its October 11, 2026 race opened in late October 2025. It closed that November 18, about ten and a half months before race day. London's public ballot for its 2027 event, a two-day "Double" run on April 24 and 25, drew 1,338,544 applicants. Results were announced in early July 2026, roughly nine and a half months before the race. Entry for these four closes six to eleven months before race day, which is two to seven months before an 18-week build would start.

What an outside count shows

A curated list like 42cal's, built around larger and better-known races, might be expected to overstate how concentrated the calendar looks. An independent count is sharper still. The Sub-3 World Marathon Rankings site tracked 81,252 finishes under three hours across 2025, drawn only from races with 1,000 or more finishers. April and October held 44.4 percent of those finishes, a sharper concentration than the 33.7 percent those two months hold on 42cal's roster. July and August combined held 4.4 percent of the fast finishes, close to 42cal's 5.2 percent of races. The site is a hobbyist ranking project rather than an official census, but the two peaks and the summer trough both hold up in a dataset built on a completely different criterion.

A marathon booked for October or April lands inside the busiest stretch of the year and the longest entry queues that come with it. A July race at the Gold Coast or in San Francisco lands in a month most of the calendar has left empty, and so does an August race in Sydney or Turku. Both run cooler than a temperate-zone summer allows, with a shorter entry queue. February and June, each with fewer than 35 races on the roster, offer the same trade-off in the shoulder seasons between the calendar's two peaks.