Race calendar · May 2027
24 ultramarathons across the US in May 2027, sorted by date. Which weekends are busiest, what the fields actually run, entry fees, and where each one starts.
May ultras play out across a country still mid-transition, which means the same calendar weekend can deliver cold predawn mountain starts in Colorado and punishing midday heat in Florida or Arizona. That range is the defining feature of the month, and it rewards runners who plan specifically for their region rather than generically for spring.
For most ultrarunners, May sits at or near the end of a winter and spring build, making it a natural target for a goal race before summer heat complicates long training days. Committing early matters here, because the entry window on some events is shorter than it first appears.
The races on this calendar vary widely in character, from multi-day road events to mountain trail loops with significant climbing, so vetting course profiles and cutoff times before you register is worth the extra hour.
What the field actually runs
How we calculate these stats: RunSesh calculates these figures from the most recent published results of past editions, sourced from RunSignup. We show aggregates only: field size, winning and median times, and the cutoff. We never publish individual finisher tables. Last updated Nov 12, 2026.
When in May
Ultramarathons are not spread evenly across May. Here is how the calendar actually falls, weekend by weekend, which is the part worth knowing before you book a trip or plan a taper around one.
By the numbers
The largest field of any May Ultra, from the most recent published results.
It is one of the busier months. May carries 24 Ultra races, against 37 in April, which is the fullest month of the year. There is a real choice of dates here, with less competition for entries than the peak of the season.
It genuinely depends on where you race. The South and desert Southwest can already be hot enough at midday to affect pacing and aid-station strategy, while higher-elevation and northern races often start cold, sometimes with unpredictable afternoon weather. Pack layers you can shed, not just the kit you want to finish in.
Start with a base that handles cold dawn temperatures, because many May ultras begin before sunrise when conditions are well below the afternoon high. A lightweight wind layer, gloves, and a hat cover the early miles, while breathable, sweat-wicking gear carries you through any heat that builds later. Check your specific course elevation before you finalize.
A full winter of structured training is the realistic minimum, which puts your build start in late November or December at the latest. That gives you enough long-run volume and back-to-back weekend mileage without rushing into peak weeks while the weather is still unpredictable. Register early to make the deadline feel real.
Yes, with homework first. May has a genuine mix of mountain, trail, and road events spread across the country, so you can find a course profile that matches what you have trained on. Check weather norms for the specific region, confirm cutoffs fit your expected pace, and look at the entry fee before you commit.
The busiest weekend is May 15 and May 16, with 7 of them. Another 2 fall on a weekday, which is worth knowing if you are traveling for one.
Across the 10 of these May ultramarathons with published results from past editions, the median finisher ran 7:32:37, and the median winning time was 5:41:53. So anything under 7:32:37 puts you in the faster half of a typical field. That is the middle of these RunSignup fields, walkers and charity entrants included, not a national average.
The median one finished 33 runners, across the 10 of these May ultramarathons with published results from past editions. Most are far smaller than the big-city events people picture, which means less crowding at the start and a friendlier field, with a last recorded finisher at 9:43:00.
California has 3, Florida has 3, Colorado has 2, New York has 2, Ohio has 2. If you are willing to travel, those are the states where a May weekend gives you the most to choose from.
Yes, 7 races around the United States get you off the pavement: 6 are trail races, and 1 mixes road and trail.
