The short answer
Build a 100K cutoff plan from the current organizer's checkpoint table, then separate moving time from stopped time. Assign each checkpoint a planned arrival, planned departure, and minimum buffer. Rehearse the schedule on comparable terrain and revise it from observed pace drift, aid-station time, fueling tolerance, darkness, and conditions.
Do not treat the finish cutoff divided by 100 km as a pace promise. A course average hides climbing, technical terrain, congestion, navigation, mandatory checks, and every minute spent stopped.
Verify the official rules first
Copy the live organizer information and date it:
- start time and wave;
- checkpoint distance;
- whether each cutoff is for arrival or departure;
- mandatory equipment checks;
- aid-station services;
- crew, drop-bag, and pacer rules;
- withdrawal and transport process;
- course changes and weather policy.
If the organizer has not published the final table, keep the plan provisional. Do not substitute a previous year's screenshot.
Build a four-clock worksheet
Each checkpoint needs four times:
- Official cutoff
- Planned arrival
- Planned departure
- Minimum acceptable departure
| Checkpoint | Distance | Official cutoff | Planned arrival | Planned departure | Buffer at departure |
|---|---|---|---|---|---|
| CP1 | ___ | ___ | ___ | ___ | ___ |
| CP2 | ___ | ___ | ___ | ___ | ___ |
| CP3 | ___ | ___ | ___ | ___ | ___ |
| CP4 | ___ | ___ | ___ | ___ | ___ |
| Finish | 100 km | ___ | ___ | — | ___ |
Departure buffer is often more useful than arrival buffer. Reaching a station ten minutes early but spending fifteen minutes there means leaving five minutes behind the original plan.
Separate moving and stopped time
Suppose a hypothetical 100K has five full aid stations. The plan assigns:
- 6 minutes at each of the first three;
- 10 minutes at the fourth;
- 8 minutes at the fifth.
Planned stopped time is 36 minutes. If the overall finish target is 15 hours, the moving-time plan must fit inside 14 hours 24 minutes before any additional contingency. This arithmetic does not prove the pace is sustainable; it only exposes what the goal requires.
Now add realistic delays:
- refill or food decision;
- toilet queue;
- mandatory gear check;
- sock or blister care;
- locating a drop bag;
- waiting for a safe trail section.
Avoid cutting all station time to create paper margin. A rushed stop that misses food, fluid, layers, or lights can cost more later.
Assign terrain jobs
Do not use one pace for the whole course. Divide the route into:
- runnable flat or smooth trail;
- sustained climb;
- technical or steep descent;
- exposed heat, cold, wind, or altitude;
- night section;
- congested single-track;
- road or track finish.
For each section, write an effort rule and a clock check. Example: "Hike the sustained climb below hard breathing; review departure buffer at CP2." This keeps the plan actionable when GPS pace becomes noisy or irrelevant.
Observational research in a Swiss 100 km road ultramarathon found that segment speeds changed across the race and varied by age group.1 A Western States analysis likewise describes course-specific pacing across many checkpoints.2 Neither study supplies a universal trail split. Use them as evidence that pace evolves, not as a percentage to copy.
Rehearse the aid-station script
Before reaching the table, know the order:
- tell the volunteer what is needed;
- refill bottles or bladder;
- collect the planned food;
- change the one item already identified;
- confirm the next section;
- leave while eating only if it is safe and permitted.
Pack the drop bag in the same order. A transparent checklist is faster than searching through choices while fatigued.
Use a long run to record:
- arrival and departure time;
- food and fluid actually taken;
- gastrointestinal symptoms;
- foot or skin problems;
- layer or light change;
- why the stop exceeded plan.
Change the cause, not merely the target time.
Fueling is part of cutoff pacing
The ISSN ultramarathon position stand gives broad nutrition and fluid ranges while emphasizing individual tolerance and progressive practice.3 Field studies report high rates of gastrointestinal symptoms in some ultramarathon cohorts and associations with reduced intake or race disruption.46
Those results do not mean one product or diet prevents stomach problems. They support practising the exact food, concentration, timing, and effort together.
Use the marathon fueling planner to make a time-based schedule visible, then adapt it for the longer event with qualified sports-nutrition input when needed. The tool cannot determine individual medical safety.
Create three plans
Plan A: rehearsed day
Uses median comparable training pace, ordinary station times, and expected conditions.
Plan B: slower early section
Protects effort, trims optional station tasks, and keeps mandatory food, fluid, gear, and safety actions.
Plan C: stop or withdraw
Defines symptoms, injury, missed cutoff, equipment failure, or unsafe conditions that end the attempt. It includes how to notify the organizer and reach official transport.
A Plan C is not pessimism. Remote events require a safe withdrawal decision before fatigue narrows judgment.
Do not chase a shrinking buffer
When the buffer falls:
- check whether GPS distance matches the organizer's checkpoint distance;
- identify whether time was lost moving or stopped;
- review effort and symptoms;
- remove only optional station friction;
- make the smallest sustainable pace adjustment;
- follow judge, marshal, and medical instructions.
An early all-out surge can turn a manageable deficit into later collapse. Neuromuscular measurements during a 156 km ultra-trail study showed substantial lower-limb fatigue across the event, with wide implications but no individual pacing prescription.7
Safety and medical stop rules
Stop and seek event medical support for confusion, fainting, severe breathing difficulty, chest pain, repeated vomiting, inability to keep fluid down, signs of heat illness, or an injury that makes normal movement unsafe.
More water is not automatically safer. Exercise-associated hyponatremia is a serious condition addressed in international consensus guidance.8 Follow the event medical team rather than trying to solve concerning symptoms with a pace calculator.
Final race card
- Rulebook and course version checked: ___
- Official cutoff is arrival / departure: ___
- Total planned stopped time: ___
- Largest contingency: ___
- Section where headlamp/layer changes: ___
- Plan B trigger: ___
- Plan C trigger and withdrawal process: ___
- Emergency contact: ___
The ultra cutoff planner can calculate each scenario. The ultra training hub can anchor the wider build.
26weeks.ai can adapt a supported 100K pathway around completed training, recovery, and the actual event date. Start training now.
This guide is educational and not medical advice. It cannot verify a course, prescribe an individual intake, diagnose symptoms, or guarantee a finish.
References
- Pacing strategy in elite and age-group 100 km ultramarathoners. 2015. (PubMed)
- Pacing in the Western States 100-Mile Endurance Run, 2006–2023. 2025. (PubMed)
- ISSN position stand on single-stage ultramarathon nutrition. 2019. (PubMed)
- Gastrointestinal symptoms, intake, and hydration in ultramarathons. 2016. (PubMed)
- Nutrition and gastrointestinal symptoms during a 56 km trail ultramarathon. 2024. (PubMed)
- Gastrointestinal distress during a 161 km ultramarathon. 2015. (PubMed)
- Strength and power fatigue during a 156 km ultra-trail event. 2026. (PubMed)
- Exercise-associated hyponatremia consensus statement. 2017. (PubMed)
- Nutrition and athletic performance position statement. 2016. (PubMed)