Boulderthon

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.