How It Works
This predictor uses the Riegel formula with exponent 1.06 to project equivalent race times across distances: T2 = T1 x (D2 / D1)^1.06. It assumes your aerobic durability and fueling are trained enough to carry your current performance curve into longer events.
The pacing strategy selector then helps frame how to distribute effort, because identical finish times can feel very different depending on whether you run even, negative split, or fast-start pacing.
Predicted marathons from a standalone 5K are often optimistic. If your long-run volume or fueling practice is limited, treat the marathon projection as a ceiling and build race pace from controlled long workouts instead.
Accuracy & Limitations
Riegel 1.06 is a strong baseline for trained runners, but outliers are common at the marathon due to glycogen depletion, heat, and pacing mistakes. A recent 10K or half marathon generally predicts marathon performance better than a 5K.
If your race history is inconsistent, cross-check goals with the Pace Chart and confirm your fitness trend using the VO2 Max Calculator before locking race-day targets.
Real-World Examples
An athlete running 45:00 for 10K may see a half prediction near 1:39 and choose a conservative negative split: first 5K at controlled effort, then small pace drops every 5K if heart rate stays stable.
Another runner with a fast 5K but low long-run volume might receive a sub-3:50 marathon prediction, yet wisely race closer to 3:58 pace to avoid late-race collapse after 30 km.
FAQ
Why does my marathon prediction look too fast?
Short-race data can overpredict long races when endurance-specific preparation is missing. Marathon readiness depends heavily on long runs, fueling practice, and pacing discipline.
Which input race gives the most reliable projection?
Use your most recent hard effort at a distance near your goal race. For marathon goals, half-marathon or strong 25-30 km workouts usually provide the best anchor.
How should I use pacing strategy with predictions?
Choose the strategy that matches your history: even pace for control, slight negative split for experienced pacing, and avoid aggressive fast starts unless your training specifically supports it.