Runners start · local time — Marathon and half marathon 7:00 a.m., 5K 7:45 a.m., 10K 8:00 a.m. (FAQ) or 8:10 a.m. (course page), Kids Run 8:15–8:25 a.m. (based on the 2026 edition)
Boulderthon is held on a Sunday in late September in Boulder, a college town at the foot of the Rocky Mountains.
The marathon, half marathon, 10K, 5K and Kids Run all take place over one weekend.
The start village and the expo are both in the downtown Pearl Street Mall area, so the pedestrian street turns into the festival site.
Elevation is about 5,335 ft (about 1,626 m), so you need to plan for the altitude.
For the 2026 edition, the total climb was 845 ft for the marathon and 381 ft for the half marathon;
the official site says the 2027 edition uses a new course and the climb is 40–50 percent lower than before.
Race reports mention that the half marathon begins with a gentle downhill of about 3.7 miles,
and the marathon and half marathon split near mile 5. The scenic stretch near the Reservoir is billed as a highlight.
It is a Boston Marathon qualifier, and the field grows every year, passing 17,000 in 2026.
Finishers receive a finisher medal and a finisher shirt.
In 2026 the marathon and 10K sold out early, so it is best to register soon.
There are several spectator zones, and reports consistently single out the local crowd energy first.
Not everyone loves it, though (one participant ran it three times and swore never again), so read the reviews too.
