I was surprised when I noticed my UTMB Index had jumped significantly without any new results. Turns out it's not a glitch.
UTMB have updated the Index algorithm and retroactively recalculated all scores from the past five years. The new parameters factor in gradient, maximum altitude, and competitive dynamics at the front of the race. The stated aim is better assessment of faster/more runnable courses, high-mountain formats, and performances in highly competitive fields.
Full write-up from UTMB here: https://utmb.world/news/Index-evolution
They've also published a video recently explaining how the Index works if you didn't already know and want the broader context: https://www.youtube.com/watch?v=XpKp3NWMsCs
How much have scores actually changed?
Here's how some of mine moved as I had previously written the old scores down:
| Race | Previous | Updated | Change |
|---|---|---|---|
| Arc of Attrition 100 miles 2026 | 498 | 529 | +6.2% |
| Run To The Sea Brighton 50k 2025 | 511 | 577 | +12.9% |
| Dark Downs 50k 2025 | 562 | 628 | +11.7% |
| Overall Index | 545 | 607 | +11.4% |
One source quotes average variance of around 2%. My scores changed by 6–13%, so treat that figure with scepticism — I'd be interested to know how others were affected!
Does it matter?
Probably not! I imagine if there's been a significant change in scores overall, the elite thresholds will also be updated to reflect this. I'm not sure if any races rely on Index scores for qualification, and if so this may be one area affected.
Beyond that, perhaps you felt a race's index score didn't truly reflect your performance it might now be a little more accurate. No system is perfect, but a retroactive recalculation of five years of scores is a fairly significant intervention for something framed as a refinement.
TL;DR: Don't panic if your UTMB Index has suddenly changed. UTMB updated the algorithm and recalculated everything.