Colorado · Marathon · Half Marathon · 10K
Boulderthon
Boulderthon is a marathon, half marathon, 10K, 5K and Kids Run event held in Boulder, Colorado. Its next confirmed date is Sunday, September 26, 2027. About 15,000 runners take part across all distances.
- Race day
- September 26, 2027
- Location
- Boulder, CO
- Field size
- ~15,000 runners
Race details
- Date
- Sunday, September 26, 2027
- Location
- Boulder, Colorado
- Distances
- Marathon, Half Marathon, 10K, 5K, Kids Run
- Field size
- About 15,000 runners
- Course
- ~5,300 ft base elevation at the foot of the Flatirons; rolling start/finish in downtown Boulder
- Registration
- boulderthon.org
Registration, course & weather
- Registration status
- Open
- Start time
- 7:00 AM MDT
- Course profile — Half Marathon
- Loop course; Road surface; 203 ft gain (official course data); USATF certified
- Course profile — Marathon
- Loop course; Road surface; 603 ft gain (official course data); USATF certified; Boston qualifier
- Typical race-day weather
- about 50°F at the start, 75% humidity, 2 mph wind (based on the 2025 race day, measured near the city center rather than the exact start line; Open-Meteo, checked October 2, 2026)
About the Boulderthon
Colorado's largest fall race weekend, with marathon-through-5K distances starting and finishing on Boulder's Pearl Street Mall beneath the Flatirons.
Rankings and notes
- Rankings and awards
- Billed as Colorado's largest fall race series and one of the largest September running weekends in the U.S.; draws runners from all 50 states and 20+ countries
More marathons in Colorado
Coming up next, by confirmed date.
-
Run Through Time Trail Marathon and Half MarathonSalida, COMarathonHalf Marathon10K5K +1 more ~3,133 runners
More races in Boulder
More upcoming races in Colorado
Keep exploring
- All races in Colorado
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- 10Ks in Colorado 70 upcoming races
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- Marathons in Colorado 13 upcoming races
- 5Ks in the United States 6,000 upcoming races
- 10Ks in the United States 2,572 upcoming races
- Half Marathons in the United States 1,668 upcoming races
- Marathons in the United States 594 upcoming races
- Fall Marathons
- September Marathons
- September races in Colorado
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- Marathons in Kansas 10 upcoming races
- Marathons in New Mexico 9 upcoming races
- Marathons in Nebraska 9 upcoming races
Guides from the RaceRove blog
- 8 min read How to Choose Your First Marathon A practical checklist for choosing a first marathon based on course, weather, cutoff, travel, field size and support.
- 7 min read How to Find a 5K, 10K, Half Marathon or Marathon Near You A practical way to find running races near you: pick a distance, decide how far you'll travel, read the listing properly and confirm the details before you register.
- 9 min read How to Run a Race in All 50 States How to plan a 50-state running challenge: set your own rules, group states into trips, build a calendar around the seasons, budget for it and keep track of every finish.
- Blog All guides Planning advice for finding, choosing and travelling to races.
Boulderthon: common questions
- When is the Boulderthon?
- The next confirmed date is Sunday, September 26, 2027.
- Where is the Boulderthon held?
- In Boulder, Colorado.
- What distances does the Boulderthon offer?
- Marathon, Half Marathon, 10K, 5K and Kids Run.
- How many people run the Boulderthon?
- About 15,000 runners across all of its distances. That figure is an estimate of the field size, not an entry cap.
- How do I register for the Boulderthon?
- Registration is handled by the organiser at boulderthon.org. Entry fees, caps and deadlines are set there.
- Is registration open for the Boulderthon?
- Yes — registration is open.
- What time does the Boulderthon start?
- 7:00 AM MDT.
- What is race-day weather usually like at the Boulderthon?
- about 50°F at the start, 75% humidity, 2 mph wind (based on the 2025 race day, measured near the city center rather than the exact start line; Open-Meteo, checked October 2, 2026).
Plan this race in RaceRove
Save it to your plan, compare it with other races, check typical race-day weather and track your 50-state progress in the interactive app.