This page explains how the Paddy Buckley schedule planner works — what it's actually calculating when you enter a target time and fatigue percentage, and why it produces the estimates it does.
The route
The Paddy Buckley Round is recognised as one of the Big Rounds in British fell running:
- England — Bob Graham Round
- Wales — Paddy Buckley Round
- Scotland — Charlie Ramsay Round
- Northern Ireland — Rankin Round
Pace model
The starting point is Naismith's Rule — the long-established formula that estimates hill time as one hour per 5 km of distance plus one hour per 600 m of climbing. It's a reasonable approximation for walking on moderate terrain, but it treats all descents as free, which isn't realistic on a round like the Paddy.
The planner uses an extended version with four parameters: base flat pace, an ascent cost, and two separate descent costs — one for runnable ground, one for steep or technical ground. The actual parameter values were fitted to the leg-by-leg splits from a reference schedule built from established Paddy completion times.
| Parameter | Value | What it means |
|---|---|---|
| Flat pace | 6:10 /km | Running pace on level ground |
| Ascent cost | 3.72 s/m | Every 100 m of climbing adds roughly the same time as an extra 1 km on the flat |
| Runnable descent | 0 s/m | Gentle slopes — time saved going down cancels effort of controlled running |
| Steep descent | 2.90 s/m | Forced braking, rocky scramble — every 100 m costs about 80% as much as an equivalent climb |
Two buckets for descent
The key judgement in the model is how to classify each section of descent. The planner uses a gradient threshold of 25% (roughly 14°) as the dividing line.
Below 25% — what you'd call runnable ridge terrain — the gravitational assist and the braking effort roughly cancel out, so the net time contribution is treated as zero. The descent from Moel Eilio to Llanberis is a good example: long and steep enough to feel fast, but consistently runnable.
At 25% and above — where you're picking a line between rocks, scrambling, or actively braking to stay upright — descent costs time. The Tryfan to Ogwen descent averages around 43% gradient and is one of the most significant time costs in this category on the round.
Calibration
The four parameter values were found by fitting the model to the reference schedule: minimising the total error across all 52 legs while keeping the model's grand total exactly equal to the schedule total. The result matches the historical splits with an average error of about 3–4 minutes per leg.
Target time
Setting a target total time doesn't change which legs are harder than others — it scales all the Naismith estimates proportionally so they add up to your target. A leg with a long climb still takes more of your total time than a short ridge hop; the relative difficulty of each leg is preserved.
The default target is a somewhat arbitrary 23:26 hr. Reduce it for a faster planned attempt; increase it for a more conservative one.
Fatigue
A flat pace model assumes you hold the same effort from start to finish. On a 100km+ mountain round, that's not realistic. Early legs tend to go faster than predicted; later legs slower. The fatigue setting lets you build this into your schedule so it reflects what is likely to actually happen rather than what would happen if you paced every leg identically.
The fatigue model works in three phases based on how long you've been moving:
The fatigue slowdown percentage you set is the gap between your plateau pace and your starting pace. At 20%, you're running 20% slower late in the race than at the start. The total time across the whole round stays the same — fatigue shifts time from early legs to late ones, it doesn't increase your target.
Set fatigue to 0% to use a flat pace throughout. The phase boundaries (2 h and 7 h by default) can be adjusted in the Advanced panel if you want to model an earlier onset or a longer build. If you don't expect a plateau (so much as a continued decline!), set second boundary to be the end of your run.
Night penalty
Moving at night on a mountain round is slower than in daylight. Reduced visibility, more careful navigation, and the accumulated effect of many hours without sleep all take their toll. The dark-hours penalty applies an additional time cost to any legs that fall within the night window.
Enter your attempt date and the planner calculates the actual sunset and sunrise times for Llanberis. A 30-minute buffer is applied at each end to account for fading light after sunset and usable light before sunrise. Without a date, it defaults to 22:00–04:30.
A leg that starts in daylight and finishes in the dark gets a partial penalty, proportional to how much of its estimated time falls in the dark window.
As with fatigue, the total time is preserved — any extra time added to night legs is taken back from daytime legs, so the overall target remains accurate.
The night penalty is applied after the fatigue adjustment. Fatigue determines the clock-time position of each leg; the dark penalty then redistributes time based on where those adjusted legs fall in the day.
Set the penalty to 0% to remove the night effect entirely. The Advanced panel allows you to override the dark window times manually — useful if you want to model a very early or very late start, or explore a winter attempt where the night window is significantly longer.