2026 Boulderthon Boulder Marathon - Sep 27 Countdown

Q: When is the 2026 Boulderthon Boulder Marathon and what time does it start?

Boulderthon is on Sunday, September 27, 2026, with the full marathon starting at 7:00 a.m. Mountain Time. The Start Village is on the Pearl Street Mall in downtown Boulder, with the start line at 21st and Pearl. The half marathon, 10K, 5K and Kids Run share the same fall weekend.

Q: How does altitude affect the Boulder Marathon?

A lot. The entire course sits over a mile above sea level (high point near 5,406 ft / 1,648 m), where the thinner air reduces available oxygen and slows paces compared with sea level. Most runners coming from lower elevations should plan for a slower-than-goal effort, hydrate aggressively and consider arriving a few days early or treating it as a destination race rather than a flat PR attempt. Use the pace calculator to set realistic splits, then add margin for the altitude.

Q: Is the Boulder Marathon a Boston qualifier?

Yes. Boulderthon is USATF-sanctioned and a Boston-qualifying race, measured by a Level A USATF course measurer, so a qualifying time here counts toward Boston Marathon entry. It is an honest but not easy qualifier — the rolling terrain and high altitude make it tougher than a flat sea-level course. Check your target on the Boston qualifying calculator.

Q: What is the time limit for the Boulder Marathon?

The full marathon has a 6-hour time limit, which requires holding roughly a 13:43 per mile (8:32 per km) pace, and the finish line closes around 2:00 p.m. Runners who expect to need more time should account for both the cutoff and the slowing effect of the altitude when planning their day.

Q: How do I register for Boulderthon?

Registration is handled online through the official Boulderthon site; there is no lottery — entry is first-come, first-served. Because Boulderthon has been one of the fastest-growing fall races in the US and typically sells out, registering early is strongly recommended, and prices rise as race day approaches. The marathon, half marathon, 10K, 5K and Kids Run are all part of the same weekend.

Q: How big is the Boulder Marathon?

The race weekend draws 15,000-plus participants across all distances, which makes the festival feel like a big-city event, but the full marathon itself is mid-sized — roughly 2,000 finishers in recent years (about 1,998 in 2025), making it Colorado's second-largest marathon. Expect a lively downtown start and finish on Pearl Street with quieter, scenic stretches on the back roads in between.

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Race Information

Race	2026 Boulderthon Boulder Marathon - Sep 27
City	Boulder
Date	2026-09-27 at 07:00
Field Size	~1,998 runners
Time Limit	6 hours
Cutoff pace	8:32/km
Timezone	America/Denver
Official Site	Boulderthon
Registration	Register

Race Day Weather

Average Temperature	16.1°C / 61°F
Humidity	39%
Wind	19.7 km/h
Rain Chance	18%
Typical Conditions	Cool, dry, high-altitude late-September Boulder morning — a crisp start around 52 degrees F (11 degrees C) at 7:00 a.m. that warms quickly under strong Colorado sun, with thin air at roughly a mile above sea level

What to Prepare: Late September in Boulder is classic Colorado fall: a chilly, dry start near 52 degrees F (11 degrees C) that climbs fast once the sun clears the Flatirons. The thin air at over 5,300 ft (1,600 m) matters more than the temperature — expect slower-than-sea-level paces and a stronger thirst, so hydrate aggressively and ease off your goal effort. Throwaway gloves and a long-sleeve you can shed early are smart, and high-altitude UV is intense, so wear sunscreen and a visor.

Based on historical averages for race week. Use our Weather Score Calculator and What to Wear Guide for personalized advice.

Wind Impact on Race Day

Wind at 19.7 km/h can affect your marathon pace by 5-15 seconds per kilometer. Headwinds slow you down exponentially — a 20 km/h wind costs more than twice a 10 km/h wind.

Calculate your wind-adjusted pace →

Race-Week Climate

Based on 20 years of race-week weather (2005-2024), MERRA-2 reanalysis

	Cooler	Typical	Warmer
Temperature	10.5°C	17°C	20.7°C
Dew point	-3.7°C	1.4°C	6°C

Wet-day chance: 18% Runnability: 85/100

Data: NASA POWER (MERRA-2 reanalysis), NASA Langley Research Center

Course Profile

Course Type	Point-to-loop city and back-roads tour
Elevation Gain	184m
Terrain	Road (paved Boulder back roads and downtown brick streets, rolling, high altitude)
Profile	A high-altitude scenic tour rather than a flat time-trial. The Start Village sits on the Pearl Street Mall between Broadway and 15th, with the start line at 21st and Pearl, and the whole course runs at over a mile above sea level (a high point near 5,406 ft / 1,648 m). Runners head out onto the quiet back roads of Boulder beneath the Flatirons foothills, with open mountain views, before winding back into downtown for a finish on the historic, brick-paved Pearl Street Mall. It is a genuinely hilly course — about +600 ft (184 m) of total gain on the redesigned 2025-onward course with steady rolling rises rather than one big climb — and the thin air is the real challenge: paces run softer than at sea level. The course is USATF-sanctioned and Boston-qualifying (measured by a Level A USATF measurer), so a BQ time counts, but the altitude and rolling terrain make it a destination experience and a tough-but-honest qualifier rather than a Berlin-flat PR machine. Boulderthon has grown fast since 2021 and typically sells out, so register early.
Boston Qualifier	Yes — Check your BQ time

Prepare for 2026 Boulderthon Boulder Marathon - Sep 27

Use our free training tools to get race-ready:

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Frequently Asked Questions

When is the 2026 Boulderthon Boulder Marathon and what time does it start?

Boulderthon is on Sunday, September 27, 2026, with the full marathon starting at 7:00 a.m. Mountain Time. The Start Village is on the Pearl Street Mall in downtown Boulder, with the start line at 21st and Pearl. The half marathon, 10K, 5K and Kids Run share the same fall weekend.

Where does the Boulderthon course go?

It is a scenic tour that starts and finishes downtown on the historic Pearl Street Mall. From the start at 21st and Pearl, runners head out onto the quiet back roads of Boulder beneath the Flatirons foothills, with open Rocky Mountain views, before winding back into downtown for a memorable finish on the brick-paved mall. Check the official course map for the current full-marathon route, as the event has refined its courses while growing.

How does altitude affect the Boulder Marathon?

A lot. The entire course sits over a mile above sea level (high point near 5,406 ft / 1,648 m), where the thinner air reduces available oxygen and slows paces compared with sea level. Most runners coming from lower elevations should plan for a slower-than-goal effort, hydrate aggressively and consider arriving a few days early or treating it as a destination race rather than a flat PR attempt. Use the pace calculator to set realistic splits, then add margin for the altitude.

Is the Boulder Marathon a Boston qualifier?

Yes. Boulderthon is USATF-sanctioned and a Boston-qualifying race, measured by a Level A USATF course measurer, so a qualifying time here counts toward Boston Marathon entry. It is an honest but not easy qualifier — the rolling terrain and high altitude make it tougher than a flat sea-level course. Check your target on the Boston qualifying calculator.

What is the time limit for the Boulder Marathon?

The full marathon has a 6-hour time limit, which requires holding roughly a 13:43 per mile (8:32 per km) pace, and the finish line closes around 2:00 p.m. Runners who expect to need more time should account for both the cutoff and the slowing effect of the altitude when planning their day.

How do I register for Boulderthon?

Registration is handled online through the official Boulderthon site; there is no lottery — entry is first-come, first-served. Because Boulderthon has been one of the fastest-growing fall races in the US and typically sells out, registering early is strongly recommended, and prices rise as race day approaches. The marathon, half marathon, 10K, 5K and Kids Run are all part of the same weekend.

How big is the Boulder Marathon?

The race weekend draws 15,000-plus participants across all distances, which makes the festival feel like a big-city event, but the full marathon itself is mid-sized — roughly 2,000 finishers in recent years (about 1,998 in 2025), making it Colorado's second-largest marathon. Expect a lively downtown start and finish on Pearl Street with quieter, scenic stretches on the back roads in between.