How is a runner’s ULTRA Index calculated?

A runner's ULTRA Index (UI) provides a measure of the racing load a runner has accumulated over the past 3 years. 

In our definition of total racing load, the effort exerted in a specific race is captured through the ULTRA Points (UP) awarded to a race result, and ULTRA Points are factored into the total racing load calculation through a decaying weight factor that helps account for the recency of a given race result.

The formula for calculating the ULTRA Index for a runner is:

Runner UI = Sum over all results in the past 3 years of ( Race result weight * Race result UP )

The calculation of a given race result UP is given here.

The race result weight aims to reduce the weight of older results in a way that avoids big jumps when a race result drops off the 3-year calculation window. More specifically, the race result weight:

• is 1 for all race results in the past 2 years
• drops linearly from 1 to 0 for results older than 2 years (up to the 3-year calculation window cutoff) 

To see how a runner's ULTRA Index is put together, let's look at some concrete examples:

Example 1: A runner has had two eligible 100K race results, 6 and 12 months ago.

Let's assume that each result has 80 UP. 

Both results are within the past 2 years, and therefore have a weight of 1.

The runner UI is 1 * 80 + 1 * 80 = 160.

Example 2: A runner has had two eligible 100K race results, 6 and 26 months ago.

Let's assume that each result has 80 UP.

The more recent result is within the last 2 years and has a weight of 1. The second result is older than 2 years - it is 2 months into the 3rd past year and therefore has a weight of 1 * (12 - 2) / 12 = 0.83.  

The runner UI in this case is 1 * 80 + 0.83 * 80 = 146.4.

Example 3: A runner has had three eligible 100K race results, 6, 18, and 30 months ago.

Let's assume that each result has 80 UP.

The two most recent results are within the last 2 years and have a weight of 1. The third result is older than 2 years - it is 6 months into the 3rd year and therefore has a weight of 1 * (12 - 6) / 12 = 0.5.

The runner UI in this case is 2 * 80 + 0.5 * 80 = 200. 

Note that, as discussed in the PI calculation methodology, backyard ultras, races with fewer than 20 participants and non-standard fixed-time races (fixed-time races other than 6h, 12h, 24h, and 48h) are ineligible for receiving ULTRA Points and are therefore excluded from the UI calculation.