After going through scores of data, race results and runner profiles, I’ve been able to narrow down exactly how long it will take you to finish the world’s oldest 100 mile trail race, the Western States 100.

The exercise started when I began to wonder how fast I would be able to complete the Ultra-Trail du Mont Blanc (UTMB). Purely for curiosity’s sake, I was visualising 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 needed to find out.

After determining how long it would take me to finish the UTMB (38 hrs 46 mins), I turned my focus to the Western States 100.

This year was my second year in the lottery. I was clinging on to the hope that my 1% chance would come through. Unfortunately, it did not.

However, that didn’t stem my enthusiasm from trying to work out how long it would take me to run from Olympic Valley in California to Auburn. Could I break 24 hours? Would I be able to cling on to finish in the Golden Hour and receive a prized bronze belt buckle for my efforts? I was determined to find out.

In order to do so, similar to the UTMB calculations, I examined the relationship between runners’ UTMB Index and their Western States finishing times. As a result, I’ve once again cracked the code.

Using the 2023 Western States results, I searched for each individual finishers’ UTMB Index and matched it with their finishing time. Of the 328 finishers, I was able to allocate 325 UTMB Index numbers. As a result, 99% 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 Western States 100?

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, Courtney Dauwalter, 2023 Western States Female Winner has a UTMB Index of 850 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 25 hrs 3 mins.

2023 Western States 100 Results

The fastest runner in the 580 Index range ran the Western States 100 in a time of 22 hrs 3 mins and the slowest runner ran a time of 29 hrs 51 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 are also displayed in the table above.

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 Western States. 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 from Olympic Valley to Auburn and tackle one of the most prestigious trail races in the world. Happy running!