Marathon du Mont-Blanc
90 km du Mont-Blanc
Chamonix → Chamonix (Planpraz)
Race guide
Updated 29 June 2026
The 90 km du Mont-Blanc is the headline distance of the Marathon du Mont-Blanc festival in Chamonix, France. Starting and finishing in the heart of Chamonix (at the Planpraz finish elevation of 1042 m), the race covers 90 km with a brutal 5864 m of total ascent, peaking at 2477 m. It is a point-to-loop route that loops the entire Chamonix valley, taking runners north along the Arve valley to Vallorcine and the Swiss border at Emosson before swinging south to Le Buet, La Flégère, and the iconic Brévent–Planpraz ridge above Chamonix. This is not a beginner ultra: with nearly 6000 m of climbing spread across 90 km of technical mountain terrain, a cut-off window that spans roughly 22 hours, and a finish on a high ridge at 1042 m (Planpraz), it demands well-rounded mountain running ability, solid night-running experience, and a disciplined race-day plan.
Course & Terrain Overview
The race departs Chamonix at 1044 m and immediately heads north-east toward the Col des Montets area, climbing steeply to 2105 m by kilometre 13 before descending to Vallorcine at 1853 m (km 19). From Vallorcine the course drops further to the Emosson dam at 1433 m (km 29) — a section that feels deceptively runnable but accumulates fatigue in the quads. The course then climbs and rolls to Le Buet at 1328 m (km 39), roughly the halfway crew point. The second half is the harder half: the climb from Le Buet to La Flégère (1640 m, km 51) is sustained and exposed, followed by the push up to Planpraz (2002 m, km 58) for the first passage. The course then drops steeply down to Les Houches/Merlet (1233 m, km 70) before the defining final section: a big climb back up to the Brévent area at 2160 m (km 82), the race's high point. The final 8 km descend to the Planpraz finish at 1042 m. Trail surfaces mix gravel paths, rooted singletrack, exposed ridge lines and rocky technical descents — full trail shoes with adequate grip and ankle support are essential.
The Decisive Climbs and Where the Race Is Won or Lost
There are three moments that define your race. First, the opening climb to Col des Montets (km 0–13, rising over 1000 m to 2105 m) sets the tone; going too hard here in the excitement of race day will cost you dearly later. Second, and most critical, is the push from Le Buet (km 39) through La Flégère (km 51) to the first Planpraz passage (km 58) — nearly 700 m of climbing in 19 km after you already have 39 km in your legs. The cut-off at Planpraz first passage is 18:00 on Friday; arriving here with time in hand separates those who will finish from those who will not. Third, the Brévent climb from Les Houches/Merlet (km 70, 1233 m) to the Brévent area (km 82, 2160 m) — nearly 930 m of climbing after 70 km — is where the race is truly decided. This section is run in darkness (cut-off is 01:30 Saturday), and runners who have not conserved energy through the middle section will slow dramatically or time out here. Budget your effort ruthlessly through km 40–70; the Brévent climb will ask for everything that remains.
Pacing & Fuelling Strategy
With 22 hours of racing on the table and cut-offs that tighten progressively, negative splitting is not realistic — but even pacing of effort (not pace) is. Hike all steep climbs from the very first ascent; running the uphills early will not save meaningful time but will destroy your legs for the second half. Target arriving at Vallorcine (km 19) well inside the 09:15 cut-off and use the crew point to restock efficiently — keep stops under three minutes. At Le Buet (km 39, cut-off 13:45) you have your last crew access before a long unsupported stretch to Les Houches/Merlet (km 70). Carry enough calories for roughly 7–8 hours of running across that gap and plan for at least 600–800 ml of water capacity given the high-altitude exposed terrain between Flégère and Planpraz. Aim for 200–300 kcal per hour from a mix of easily digestible gels, bars, and real food at checkpoints. Salt intake matters on a race this long; prioritise savoury options at crew points. The Les Houches/Merlet crew point (km 70, cut-off 21:00) is your final resupply — after this you face the Brévent climb in the dark, so headtorch batteries, an extra layer, and topped-up calories are non-negotiable before leaving.
Conditions to Expect
The race runs in mid-June in the Mont-Blanc massif, which means conditions are highly variable and altitude matters. At valley level (Chamonix, Vallorcine, Le Buet) temperatures can range from 5–20°C, but on the exposed ridges above 2000 m — the Col des Montets area, La Flégère, Planpraz, and especially the Brévent at 2160 m — it can be significantly colder, particularly during the overnight section from roughly 21:00 onward. Wind and cloud can arrive rapidly on the high sections. A mandatory kit list applies; follow it strictly. Rain is common in June and will make the rocky descents off Brévent and the technical trail near Planpraz noticeably more demanding. Expect full darkness from around Les Houches onward and plan your lighting accordingly — the Brévent climb and the final descent to Planpraz must be run in the dark. Snow on the upper trails is possible depending on the season; check race communications in the days before the event for any course modifications.
Race 90 km du Mont-Blanc with Crux
Get the strategy, fuelling and crew plan dialled for this exact course — built from the real route, climbs and cut-offs. Your first race is free.
Plan this race — freeCourse profile
Checkpoints & cut-offs
✓ Course data verified against the official source (2026-07-05) · official source
0 km · 1044 m · —
12.7 km · 2142 m · —
18 km · 1850 m · Fri 09:35
28.5 km · 1354 m · Fri 11:35
35.1 km · 1965 m · Fri 13:05
40.6 km · 1412 m · Fri 15:05
44.7 km · 1874 m · Fri 16:05
48.4 km · 1202 m · —
60.1 km · 1859 m · Fri 20:20
69.7 km · 1233 m · Fri 22:20
75.2 km · 1616 m · Sat 00:50
81.2 km · 2142 m · Sat 02:50
88.8 km · 1085 m · Sat 05:05
More races
More independent
More in France
Similar distance (100 km–100 miles)
Racing 90 km du Mont-Blanc?
Get a complete race strategy — pacing, fuelling, crew plan and the crux moments — built on this exact course.
Plan your race in Crux →Strava is your training. Crux is your races.