I’m on Reddit’s r/ultrarunning regularly and it seems like not a week goes by that someone does ask a question along these lines. Typically, it’s someone relatively new and wants to know whether they can finish a 50k, 100 miler, or whatever race they’ve got their eye on. It’s a pretty supportive group on there so unless the person has virtually no running experience, the comments will generally tend to say go for it.

And I don’t have a problem with that. There’s nothing wrong with setting outrageous goals to motivate yourself. Even if you don’t accomplish them, you still end up doing things you never thought were possible.

I guess I struggle with how these questions and responses are typically framed as a binary outcome: yes or no. Finish or DNF. In reality, we’re all on the spectrum somewhere between never in a million years and virtually certain. The likelihood of us finishing any given ultra will depend on our fitness and experience. The following charts are how I think experience translates into a successful finish at a typical ultra. If a race is extra hard (i.e. at altitude or across a desert), then you probably want to knock 10-20 percentage points off your likelihood of finishing.

Generally speaking, I don’t think you need too much experience for a successful 50k finish. I think an athletic, non-runner could roll right off the couch and have an almost 50/50 chance of finishing with the right coaching and race strategies. I’m not sure you can ever be a complete lock to finish an ultra, but 5+ years and 30+ finishes will probably get you up to the 98-99% range assuming no injuries or completely bonkers weather.

For a 50 mile race, you obviously need a bit more experience and fitness. There’s still a chance your athletic, non-running friend can finish, however the likelihood has just dropped quit a bit. Your very experienced, non-injured friend might be able to get his odds up to a 95% chance of finishing, but probably not above.

I’m probably being a little generous to put our athletic, non-runner on this chart at all, but he or she’s still got a chance. At the other end of the spectrum, the most experienced runners out there can probably only get up to a 90% chance. There’s just so many things that can go wrong, it’s hard to put your chances any better than this.

And honestly, I think that’s the draw for a lot of us to any of these distances. The unknown of not just how well we will do on race day, but whether we can even finish the race at all. Just because my charts above don’t give you a good chance to finish a given race, doesn’t mean you won’t. As the great Wayne Gretzky once said, you miss 100% of the shots you never take.