Trail ultramarathon · Croatia
2–4 April 2027 · Umag, Istria, Croatia
21K: Sun, 4 April 2027
A long-running Adriatic ultra weekend crossing Istrian hill towns, coastal trails, and inland forest tracks before finishing by the sea.
Entry · 21K · 2027 edition
First come, first served until Sun 31 Jan 2027, 23:59 CET or until places run out. Open on the organizer's page on 30 Sep 2026, which does not say how many places are left.
Subscribe to these entry dates (updates when the organizer's dates change and we recheck them) · Download .ics. Separate from any training calendar; remove it any time in your calendar app.
From the organizer's page, checked 30 Sep 2026. TrailSplits does not know whether you have a place; the organizer is the final word.
Istria 100 by UTMB is a trail ultramarathon scheduled for 2–4 April 2027 in Umag, Istria, Croatia. TrailSplits currently includes 3 mapped courses for this event, with course maps, elevation profiles, weather context, and pacing tools for the uploaded GPX data.
How to get a place: Registration for the 2027 edition is open: UTMB Index holders from 16 June 2026, everyone from 18 June 2026 until 31 January 2027 or sell-out; no waiting list. Organizer's page, checked Wednesday 30 September 2026.
TrailSplits is a free, independent route & pacing companion — not the official race. Visit the official Istria 100 by UTMB site →
Finishing 21K earns 1 Running Stone (20K category) toward the UTMB World Series Finals lottery. How Running Stones work.
Racing more than once next year? Add 21K to a season and see whether your races work together.
Inspect the official course track on a topographic map, through its elevation profile, or in 3D.
› running direction two lines: out and back on the same path kilometres
Selected distance
Vert-focused blueprint with route-finder links into the Planner.
Prepare and return
Keep this course, its training plan, calendar and future course updates together in your private My Races page. Saving does not publish your workouts, pace or progress.
Race route lab
Open the official course in Planner, then choose a nearby start point to build a shorter loop that matches the course demand. This course averages about 7.3 m climb per km.
Sun, 4 April 2027
Send to your watch
Get the official course as a clean GPX or a Garmin TCX course, with step-by-step instructions to load it onto a Garmin, COROS, Suunto, Wahoo, or Komoot — free, no account needed.
Compare your training
See how faithfully your rehearsal route matches the real race. The official course for 21K loads as Route A — upload your training route to compare distance, elevation gain, estimated time, and how much of the course you actually cover.
Course analysis
See the 21K course broken into its major climbs and descents in order — length, gain, average grade, and steepness — so you know where the crux is and how to pace and fuel it.
Race-week reminders
A free browser notification in the final week — the course crux, the weather window, and loading the GPX onto your watch. No app, no email, no account.
Istria 100 by UTMB 2027 races run 2–4 April 2027 in Umag, Istria, Croatia; the 21K is on Sun, 4 April 2027. Check the official race site for registration deadlines and final details.
3 distances (21.5–168.2 km). The longest course is 168.2 km with about 7,140 m of vertical gain — a demanding mountain course.
The 168K course has a 45-hour cut-off, an average of 16.1 min/km to finish in time. TrailSplits' cut-off pacer shows the buffer at each aid station.
Yes. TrailSplits gives you the course map, an interactive elevation profile, a 3D flyover and a downloadable GPX for every mapped distance — free and with no sign-up.
Each distance has a free, course-specific 16-week training plan built around its distance, vertical gain and cut-offs, plus a pace and cut-off calculator.
No. TrailSplits is a free, independent route and pacing companion. For registration and official rules, visit https://istria.utmb.world/.
Load the GPX directly into TrailSplits for surface analysis and terrain intel.