Boulderthon
The Lowdown
Boulderthon is an annual road race weekend held every fall in Boulder, Colorado, anchored by a Boston-qualifying marathon on a USATF-certified, Level A course. Now presented by lululemon, the sixth edition takes place on September 27, 2026, starting at 7:00 AM from downtown Boulder near Pearl Street, climbing out past the Boulder Reservoir with sweeping views of the Flatiron mountains before finishing back downtown on the Pearl Street Mall. The marathon has been named among the Best Fall Marathons by Runner's World, and the overall weekend has attracted more than 15,000 runners from all 50 states and over a dozen countries, plus one of the largest downtown running expos in the country. Alongside the marathon, Boulderthon also stages a half marathon, an all-roads 10K presented by Cheribundi, the Heart to Heart 5K presented by Boulder Community Health (with a prize purse of more than USD 40,000, one of the largest in the country for the distance), and a Kids Run. Marathon runners must be at least 13 years old and finish within the 2:00 PM course cutoff. Boulderthon has sold out every year, so early registration is recommended.
Race Day
Weather Forecast
Elevation
Terrain Profile
Moderate rolling hills
Participants
Field Size
Medium-sized race
Crowd Rating
Spectator Support
Excellent spectator turnout
Boston Qualifier
This race is a certified Boston Marathon qualifying event. Achieve your qualifying standard here on a verified course.
Pearl Street Mall - historic pedestrian mall hosting the Start Village, expo, and finish festival
Boulder Reservoir - marathon and half marathon course landmark with Flatiron mountain views
Flatiron Mountains - iconic rock formations visible throughout the course
Valmont City Park - 10K course landmark
Downtown Boulder finish festival - live music and the Epic After Party presented by Athletic Brewing
Other distances available during the event weekend:
Boulder, Colorado, United States
US
Average rate for 3-star accommodations near the start line
Eligibility
- Minimum age 13 for the marathon
- Minimum age 9 for the half marathon
Required Documents
- Photo ID and the QR code from the final race confirmation email are required at the Race Expo to collect a bib
Entry Methods
- Online registration via Let's Do This (official registration partner)
- General entry and VIP package options; charity and team entries also available
Cancellation & Refund Policy
Entries are non-refundable; check the official registration page for deferral/transfer terms before registering
Presented by lululemon starting with the 2026 edition, which includes a branded finisher long-sleeve for all participants.
Ranked a Top 10 marathon in the US by USA Today for three consecutive years, and named among the Best Fall Marathons by Runner's World.
The 2025 marathon drew roughly 2,700 marathon finishers as part of an overall weekend of more than 15,000 runners across all distances, with race-day temperatures in the 50s-70s Fahrenheit.
Organized by the nonprofit Stronger Faster Boulder Co.; the organizers estimate roughly USD 23 million in annual economic impact for the city of Boulder.
New for 2026: a redesigned marathon course reducing total elevation gain by roughly 40-50% versus prior editions.
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Community
Stories, tips, and race-day snapshots from runners who have tackled this course.
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