Race Pace Planner
Plan your race with per-km splits, pacing strategy, fatigue simulation, and a printable wristband.
The Race Pace Planner generates a detailed split table for your target race. Choose your distance, enter your goal time, and select a pacing strategy. The fatigue model simulates how your body naturally slows down over distance, and the wall predictor estimates where glycogen depletion may impact your performance.
Plan Your Race Pace
This calculator is for informational purposes only. Actual race performance depends on many factors including training, weather, terrain, nutrition, and race-day conditions. Always consult a coach or physician before following a race plan.
Pacing Strategies Explained
Your pacing strategy can make or break your race. Research by Abbiss & Laursen (2008) shows that even or slightly negative splits are associated with the best performances in endurance events.
Even Splits
Even splits mean maintaining the same pace throughout the race. This is metabolically efficient because your body uses fuel at a constant rate. Recommended for experienced runners who know their pace well.
Negative Splits
Negative splits mean running the second half faster than the first. This conservative approach reduces the risk of glycogen depletion and allows you to pass tiring competitors in the final kilometers. Most world records are set with slight negative splits.
Positive Splits
Positive splits mean starting faster and gradually slowing down. While this is what happens naturally to most recreational runners, it's less efficient and increases the risk of hitting the wall in longer races. However, it can work well for shorter distances (5K-10K).
The Marathon Wall
The "wall" is a phenomenon that occurs when your body's glycogen stores become depleted during a long-distance race, typically between km 28 and 35 in a marathon. Your body stores approximately 2,000 kcal of glycogen in muscles and liver — enough for roughly 90-120 minutes of intense running (Rapoport 2010).
- •Glycogen stores: your muscles store about 400-500g of glycogen (1,600-2,000 kcal). At marathon pace, you burn approximately 60-80g of carbs per hour.
- •Long runs: regular runs of 30-35 km at easy pace teach your body to burn fat more efficiently and delay glycogen depletion.
- •Carb-loading: increasing carbohydrate intake to 8-10 g/kg/day for 2-3 days before the race can maximize glycogen stores by 20-40%.
- •Pacing: starting too fast accelerates glycogen depletion. An even or slightly negative split strategy is the best defense against the wall.
Running Hills on Race Day
When running uphill, focus on effort rather than pace. A general rule is to lose about 12-15 seconds per km for every 1% of gradient. On downhill sections, you can gain some of that back, but don't overstride — this causes eccentric muscle damage that will slow you down later. The best strategy is to maintain a constant perceived effort throughout, letting your pace naturally adjust to the terrain.