After going through scores of data, race results and UTMB runner profiles, I’ve been able to narrow down exactly how long it will take you to finish the Ultra-Trail du Mont Blanc (UTMB).

The exercise started when I began to wonder how fast I would be able to complete the UTMB. Purely for curiosity sake, I started to visualise myself running (stumbling) across the finish line in Chamonix, France. It was early morning and there were people in the streets drinking coffee and tucking into breakfast, or lunch. Actually it was still dark because it was 3am on Sunday morning. Now I’m not sure. I’m not sure because I don’t know how long it’s gonna take! I need to find out. 

During my calculations of which event(s) are the easiest to complete in order to qualify for the UTMB, I calculated the David King Difficulty Ranking Scale. I plugged in my recent race result figures and found that although this was a good metric for comparing events, this wasn’t the best way to measure the duration of my impending UTMB adventure.

Looking for greater accuracy in order to assist my fellow runners (and also myself), I examined the relationship between runners UTMB Index and their UTMB finishing times. As a result, I think I’ve cracked the code on how long it will take you to finish the big one, the UTMB.

Using the 2023 UTMB results, I searched for each individual finishers’ UTMB Index and matched it with their finishing time. This took an extraordinarily long time. Of the 1758 finishers, I was able to allocate 1706 UTMB Index numbers. As a result, 97% of the runners have been included in the analysis. I then was able to determine what the likely time range for each UTMB Index was.

So, how long will it take to finish the UTMB?

First, you need a UTMB Index.

A UTMB Index is a ranking given to everyone that finishes a UTMB World Series event or a UTMB Index race. A UTMB World Series event is one in which you also receive Running stones and includes races like Ultra-Trail Australia, Western States, Eiger Ultra-Trail and Ultra-Trail Snowdonia. For a full list, click HERE.

A UTMB index race is not a UTMB World Series event but one that still awards a UTMB Index to finishers. For a full list of UTMB index races, click HERE.

Once you have completed a UTMB Index race or a UTMB World Series event, you are awarded a ranking (Index) based on how well you finish. There are separate categories for each event type; 20km, 50km, 100km and 100mi. Each category is weighted differently based on its difficulty to give you your current UTMB index. If you get better results, your index goes up. Do worse, goes down. If you don’t know what your number is, look for it HERE.

Your overall UTMB Index number (not the race specific number) is then used to calculate your expected finish time. 

For example, Jim Walmsley, 2023 UTMB Winner has a UTMB Index of 937 at the time of writing. This consists of different ratings for the different categories but the overall Index is the one we’ll use for simplicity.

But what if I don’t have a UTMB Index?

Well, if you haven’t completed a UTMB Index race or a UTMB World Series event, you’ll have to make your best estimate. I’d suggest looking up which of the races you’re most familiar with and comparing yourself with someone of a similar standard. Or, compare an event you’ve done with a UTMB Index race or a UTMB World Series event and compare your finish time with a runner in those events. 

In both instances, look up that runner HERE and see what Index they were awarded. Use that to calculate a rough UTMB Index.

Now that I have a UTMB Index…

You can determine exactly how long it will take you!

I looked up my UTMB Index and found it to be 580. Not too shabby (but not amazing either!).

I then looked up 580 on the below table (Left Column) and found the average expected finish time to be 38 hrs 46 min.

2023 Ultra-Trail du Mont Blanc Results

The fastest runner in the 580-599 range ran a UTMB time of 31 hrs 5 mins and the slowest runner ran a time of 45 hrs 50 mins.

I’ve also included (for those stats geeks!) the standard deviation for each UTMB Index range. Runners finishing 34% better than the Average (Median) and 34% worse than Average.

It’s also nice to observe what finishers’ times were that have a slightly better (and worse) UTMB Index than yourself.

Remember, these are just estimates based on your current UTMB index and where other similar runners to you have finished the 2023 UTMB. If you feel as though you are running a little quicker than when you received your UTMB Index score(s) or a little slower, adjust accordingly. Other considerations should also be made for weather conditions and any minor course changes as this will likely change from year to year.

Hopefully these can be used as a guide for you and your crew to get you around the Mont Blanc Massif and tackle one of the most daunting trail races in the world. Happy running!