Races Marathon · Denver, USA
Colfax Marathon
Colfax Marathon is a flat marathon in Denver, USA, held each May. City parks and a run through a working fire station — the course is gentle; the mile-high altitude is not. May in Denver is 8-18C and dry; altitude costs unacclimated runners several seconds per kilometre. Flat courses like Denver's reward metronomic pacing — the danger is going out faster than goal pace because it feels cheap early.
Page rebuilt 2026-10-01 · race facts not independently verified — confirm dates and entries on the official race site
When
May
every year
Course
flat
Marathon
Conditions
May in Denver is 8-18C and dry; altitude costs unacclimated runners several seconds per kilometre.
Racing this course well
City parks and a run through a working fire station — the course is gentle; the mile-high altitude is not.
Flat courses like Denver's reward metronomic pacing — the danger is going out faster than goal pace because it feels cheap early.
Pick your goal for Denver
Pace charts, weekly structure and timelines for the most common marathon goals:
We don’t hold a confirmed date for this edition, so any countdown comes from the date you enter here.
Build your training around Colfax Marathon.
RunV works backwards from race day to today and rearranges the weeks when life interrupts. It does not adapt to this specific course — the pacing guidance above is where the course knowledge is.
Everything above stays free and complete — this is an optional next step, not a paywall.
Asked often
- When is the Colfax Marathon?
- It is held each May in Denver, USA. Check the official Colfax Marathon site for the exact date and entry windows.
- Is the Colfax Marathon course flat?
- City parks and a run through a working fire station — the course is gentle; the mile-high altitude is not.
- How should I train for the Colfax Marathon?
- Match your preparation to Colfax Marathon's profile and the May weather, then protect consistency — RunV's adaptive plan recalibrates after every run so one bad week never derails the block.
Not sure what to target? Predict your marathon time from a recent race →
More marathon races
Build for Denver — around your actual life
RunV engineers your block backwards from race day in May — and rebuilds it every time training doesn't go to script.
