A trail runner on a grassy ridge above a sea of clouds

Eryri by UTMB (ex Ultra-Trail Snowdonia)

Eryri by UTMB, formerly Ultra-Trail Snowdonia, is a mountain ultra based in Llanberis, in the Eryri range of north Wales. It offers five formats from 22 km to 163 km and forms part of the UTMB World Series.

Prepare for Eryri by UTMB

A plan built from your answers and your race date.

trail training plan

The race is run in the heart of Eryri, the mountain range of north Wales, with Llanberis as its base. The terrain is classic Welsh mountain ground: rocky ridges, stony paths, very steep grassy slopes and boggy sections. The routes climb hard and drop sharply, leaving few genuinely runnable stretches.

Five formats make up the programme: Eryri 100M over 163 km with 9,200 m of ascent, Eryri 100K over 106 km and 5,400 m, Eryri 80K over 78 km and 2,500 m, Eryri 50K over 56 km and 3,400 m, and Eryri 25K over 22 km and 1,100 m.

The formats

5 formats on the program.

Format	Distance	Vertical gain
Eryri 100M	101 mi	9,200 m
Eryri 100K	66 mi	5,400 m
Eryri 80K	48 mi	2,500 m
Eryri 50K	35 mi	3,400 m
Eryri 25K	14 mi	1,100 m

Organizer information, checked on September 21, 2026 · eryri.utmb.world

When to start

At this distance, a build usually runs 12 to 24 weeks. The 2027 date is not published, so counting back from May puts the start around November 23, 2026.

These ranges are working conventions, not a research finding — no trial has compared plan lengths against each other. What matters more is that the plan was built for the weeks you actually have, rather than shrunk down from a longer one.

How to choose your start date

When to start

November 23, 2026

→ February 15, 2027

Worth reading before you enter

Races and distances Trail distances: what changes off the road Distance stops being the useful number. What decides a trail race is how long you are out, how much you climb, and how much the descents have wrecked your legs by the end. Read Training Eating and drinking: what’s proven, what isn’t This is where confident advice most often runs ahead of the evidence. Some of it is well tested. Some is opinion wearing a number. And one common habit can kill you. Read Races and distances When to start preparing your race Most plans fail before the first session, because the block started too late and everything had to be squeezed. Counting back from the date is the dullest and most useful thing you will do. Read

Questions

What is the date of Eryri by UTMB (ex Ultra-Trail Snowdonia) in 2027?

The organizer has not published the 2027 date for Eryri by UTMB (ex Ultra-Trail Snowdonia) yet. The race is usually held in May, in Llanberis.

What distances does Eryri by UTMB offer?

Five formats are available: 163 km with 9,200 m of ascent, 106 km with 5,400 m, 78 km with 2,500 m, 56 km with 3,400 m, and 22 km with 1,100 m. All of them start from Llanberis.

How hard is Eryri by UTMB?

The climbing relative to distance is very high, particularly on the 163 km and 56 km races. Solid experience of technical mountain ground and steep hiking is needed for anything beyond the 25K format.

Other races

This list keeps growing; it draws no line. A race that is missing is prepared for in exactly the same way.

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