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Ultra Pacing Calculator

Plan an ultra finish time that accounts for climb, terrain and fade.

How it is calculated

Moving time is built in steps. Flat time is distance × flat pace (km and decimal minutes per km, so 6.5 is 6:30). Climb time follows Naismith's rule as the tool applies it: 10 minutes per 100 m of ascent. Their sum is multiplied by a terrain factor: road 1.00, trail 1.15, technical 1.30; an unrecognised terrain falls back to trail. A fade factor then adds 2 % per 10 km beyond 42.195 km: fade = 1 + 0.02 × (distance − 42.195) ÷ 10. Aid-station minutes are added after the fade, so finish time is (flat + climb) × terrain × fade + aid minutes. Average pace and speed are taken over the whole time including stops. Distance must be above 0 and at most 1000 km, ascent 0 to 30,000 m, flat pace 2 to 40 min/km, and aid time (required, 0 if none) 0 to 1440 minutes; otherwise there is no result.

Worked example

50 km, 1,500 m of ascent, flat pace 6.0 min/km, trail terrain, 30 minutes at aid stations. Flat time: 50 × 6 = 300 min. Climb: 1,500 ÷ 100 × 10 = 150 min. Terrain: (300 + 150) × 1.15 = 517.5 min. Fade: 1 + 0.02 × (50 − 42.195) ÷ 10 = 1.0156, shown as 1.02x. Moving time 8:45:35. Adding 30 minutes of stops gives a finish time of 9:15:35, an average pace of 11:07 /km and 5.40 km/h overall.

Try this example →

Common mistakes

  • Typing the flat pace as 6.30 for 6:30. The field is decimal minutes, so 6.30 is 6 minutes 18 seconds; use 6.5. The difference here is about 18 minutes (9:33:06 instead of 9:15:35 for 6.3 versus 6.0).
  • Entering a flat pace from a short fast race. It should be the pace you could sustain on flat road for hours, not your 10K pace.
  • Entering ascent in feet. Elevation gain is in metres: typing 4,900 ft instead of 1,500 m turns the same race into 15:52:41.
  • Adding aid-station time to the pace as well. The aid field is the total minutes stopped for the whole race and is added once after the fade; leaving it empty gives no result, so enter 0 if you plan no stops.
  • Treating the output as a per-section plan. It gives one overall estimate with a single terrain multiplier (which also scales the climb time), so a course mixing road and technical parts needs a rough average choice.

About this calculator

Pacing an ultramarathon is far more complex than pacing a road race because elevation gain, technical terrain, aid-station stops and cumulative fatigue all interact to slow a runner well below their flat-ground pace, and that slowdown compounds as the distance stretches past marathon length. A working ultra-pacing model starts from a known flat pace, adds time penalties for climbing (often modeled similarly to Naismith's rule, which adds fixed time per unit of elevation gain), applies a terrain-difficulty multiplier for trail versus technical singletrack, accounts for planned time at aid stations, and layers on a late-race fade factor to reflect the fact that even well-trained ultrarunners slow disproportionately in the final miles.

Ultrarunners and their coaches use this kind of model to build a mile-by-mile or segment-by-segment pacing plan before a race, to set realistic cutoff-time targets, and to decide how much time buffer to bank early against aid-station cutoffs later in a race. It's also used in reverse — plugging in a goal finish time to see what average pace and effort level is actually required given the course's profile.

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