How are Kona Slots Allocated?

If you go to the Hawaii Qualification section of next week’s Ironman Los Cabos website you will find instructions for the allocation of Kona slots to age groups. You can read them there, but fundamentally slots are allocated in proportion to age group size with a minimum of one slot per category. Sounds simple, but replicating this process in software so that I can predict slot allocations for future races, such as Los Cabos, has proved much harder than anticipated.

I started playing with ideas earlier in the week, New Zealand was my test bad having recently imported all its Kona qualification data into the Ironman database. I trialled different solutions in Excel and after a morning with the numbers had a method that fairly distributed all slots with a minimum of one, but required tweaking for each race and, more importantly, didn’t match New Zealand’s allocations. It was a solution, just not the solution, and I’d reached the limits of my Excel skills.

Ironman New Zealand 2013: Kona Slot Distribution Graph

The Los Cabos guidelines gives an example that if 8% of the Age Group starters are Female 40-44, then 8% of the slots are allocated to the Female 40-44 category, but if I compared the distribution of slots in New Zealand 2013 to the distribution of athletes in Age Groups, as in the graph above, the match was poor. I wondered if the actual allocation process was, at least in part, manual with race organisers adjusting the allocations by hand to make their numbers work. That, or I was missing something obvious.

Ironman New Zealand 2013: Kona Slot Distribution

Allowing for the fact the figures above include a couple of age group roll downs (male and female 70-74 slots rolled to other age groups) the allocation tends to underrepresent the largest age groups and overrepresent the smallest. I can see some sense in that – it helps prevent the major male age groups taking all the slots. I was still interested to see if I could come up with a better distribution, either closer to the actual numbers or more accurately proportional to the age groups.

I tried several methods – you can skip this paragraph if you’re not interested in the more technical details – all based upon the principle of calculating the number of age groupers per slot and then assigning slots to age groups based on this number. For example, at Ironman New Zealand 2013 there were 1,284 age groupers on the start line and 50 slots giving 25.7 age groupers per slot, so in the male 40-44 age group with 202 members there’s potentially room for 7.86 slots. By assigning slots in rounds, giving one to each age group with space from largest to smallest, I ensured each age group took a fair share. Refinement brought the numbers closer to the actual proportions, but the approach I finally settled on assigned each age group a number of slots proportional to its size and then iteratively adjusted the distribution until the correct total number of slots were allocated. The results are shown below.

Ironman New Zealand 2013: Kona Slot Alternative Distribution Graph

My allocation doesn’t match the final slot distribution, but it more closely matches the competitor distribution. I’m no nearer to replicating the methods used by Ironman, but if they are at the organiser’s discretion I may never be. What I have is a means to estimate future distributions, such as Ironman Melbourne below, on the basis of athlete numbers.

Ironman Melbourne 2013: Predicted Kona Slots

We’ll see how my predictions stand in two week’s time. With more slots to distribute they’re likely to be more accurate, but we can anticipate the largest groups having fewer slots and some of the smallest groups having more. Whatever method Ironman uses their actual distributions don’t seem to match the precise wording of their allocation policy, but I still can’t help thinking I’ve missed something obvious.

All Ironman Results and Statistics

A growing collection of results and statistics for the whole Ironman race calendar.

Find out what it takes to place in your age group or to qualify for the Ironman Worlds Championships in Kona.


  • Nadine

    This may or may not help, the slots not taken that transferred to other age groups went to male 40-44 and female 35-39. We had thought the female one might have gone to 40-44 (maybe that was just my age groups wishful thinking) as it is the biggest female age group. Although we did have 3 slots already and I’m pretty sure there was only 2 last year for the same/similar sized field.

  • Thanks – does help. Not least because it let me test someone else’s solution with some more numbers:

    This site has got the WTC version working, nearly perfectly although it over-allocated with 2011 data and the IMNZ 2013 allocation doesn’t quite match what it produces. That said these are both areas where a degree of discretion would quickly have resulted in the actual distribution. Funnily enough, he also hits on roughly the same optimised solution for more closely matching the proportions of the age groups.


  • Nadine

    Pleased I could help, just remembered too, were you aware that they added 10 slots a few weeks out from the race? Means there was 50 slots rather than the usual 40. Hope that doesn’t play havoc with the conclusions you have come too

  • Tim Bishop

    Russ. Have you found the final Kona allocations from Los Cabos? I didn’t go to the roll down as wasn’t taking mine, but would be interested to see where they went. In all your analysis by the way, are you aware that in North America they skew the whole process towards the women, so the women’s AG’s get allocated proportionately more slots. In Utah they told me this was to try and increase the number of women at Kona… I pointed out that the correct and fair way to do this was to get more women racing in the qualifiers, rather than to actively discriminate against the men. Not something the WTC publicises, but a significant factor if you are looking to qualify and don’t know about it.

  • Tim,

    Nope, not found a thing on the actual Los Cabos distribution and roll down, nothing on the official sites and not seen any details elsewhere. Ridiculous really that they don’t publish and make more of the official qualifiers at each race – there’d be plenty of interest among age groupers… As it is I’m reliant on someone there having noted the numbers/times or the few races, like new Zealand, that actually post their qualifiers. I do know the provisional allocation they put online is completely wrong – doesn’t match any kind of distribution algorithm.

    Since Los Cabos I’ve found a new algorithm that does what you say, gives more slots to the women than their actual proportion of the field, and it seems to match most Ironman races I’ve tested it against. The way they do it at the moment is not truly proportional, it favours the smaller age groups slightly. Not fully tested it against European numbers to see how it compares.

    It should be a pretty safe bet that you’d have qualified without roll down in Los Cabos though, pretty certain there were 2 slots.


  • Tim Bishop

    The smaller AGs are favoured by the “at least one slot” policy, which is fair enough and is well publicised. The bias towards women is, in my view, completely inequitable and unjustifiable and the fact that they don’t mention it anywhere is arguably misrepresentation. I seem to recall in Utah that it took what should have been 6 slots in M45 down to 4 slots. Big difference. I definitely clean qualified in Los Cabos, but out of interest wanted to check where it rolled to and to see if a few other people I met over there qualified or not. There was much to commend in Los Cabos, but information was woeful (they didn’t even manage a race program), so I won’t expect to see this any time soon!

  • I am very curious about the actual WTC allocation implementation, because I am quite certain that it is not actually what people think it is. I have written the calculator at, and while the WTC emulator is close, it usually is off by a slot here or there. And I cannot for the life of me figure out what is going on. See this post on slowtwitch for more:

    I would like to get more raw outputs from the WTC spreadsheet, such as this picture here, so if you have any of this please forward and I will add that data to the pre-populated data in my calculator.

    This picture shows the true WTC algorithm output, before slots have rolled out of AGs and into other AGs as happened in your IMNZ 2013 data above, effectively corrupting the true WTC algorithm.

    I don’t understand why WTC isn’t transparent about their algorithm. What do they have to hide?

  • Kyle,

    What do they have to hide is a great question. Playing with the results data as I have been I often wonder why they don’t indicate DNS, DNF, DQs etc on the results; or why they don’t mark the Kona qualifiers for every race. There is a lot of information that age groupers would be interested in, facts and figures that help build a picture of the Kona qualification process. The slot allocation is part of that – like you I’ve tried to figure it out and come up with my own ‘better’ allocation that seems to match their wording more closely.

    The problem with the numbers I have is that most races upload their bib list to and it’s impossible to distinguish a DNS from a DNF in the swim. For the most part that probably accounts for a relatively small number of athletes, but it could be enough to throw off the algorithm still. I can easily give you the age group counts for about 60 Ironman races now and I can indicate how many have no swim time (so probably a DNS). There are a few races where I’ve been able to get results from a third party timing system and correctly flag the DNSs – let me see if I can pull that info out for you. The difficult part then is finding the official slot allocation for the race – that often seems to disappear too.

    Great work with the calculator. I’m happy to send you any data I can that’ll help refine the algorithm. I have to admit I do wonder about this supposed spreadsheet WTC uses and whether in fact there aren’t different versions or variations out there, or race officials adjusting the output. I agree – clarity would be good.