Marathon Time Predictor
Predict marathon finish time from a recent 5K or 10K result using the Riegel formula t2 = t1 x (d2/d1)^1.06.
Returns projected time and required pace.
Marathon finish time prediction uses your recent race performances or training data to estimate your 26.2-mile (42.195 km) finish time. Several well-validated formulas exist, each with different strengths depending on your available data.
Formula 1 — Riegel’s Formula (most popular): T₂ = T₁ × (D₂ ÷ D₁)^1.06 Where T₁ = known finish time, D₁ = known race distance, D₂ = marathon distance, T₂ = predicted marathon time.
The 1.06 exponent accounts for the fact that pace slows as distance increases (the “fatigue factor”).
Formula 2 — Pete Riegel (simplified for common distances):
| Known Race | Multiply by |
|---|---|
| 5K time | 8.80 |
| 10K time | 4.67 |
| Half marathon time | 2.09 |
Formula 3 — VO₂max based: Marathon Pace (min/mile) ≈ 29.54 + 5.000/VO₂max × 60
Worked example: You recently ran a half marathon in 1:52:30 (6,750 seconds). Predict marathon time.
Using Riegel: T₂ = 6,750 × (42.195 ÷ 21.0975)^1.06 = 6,750 × (2.0)^1.06 = 6,750 × 2.085 = 14,074 seconds = 3:54:34
Using the multiplier: 1:52:30 × 2.09 = 3:55:18 (close agreement)
Pacing strategy for 3:55 target:
- Even split: Each mile at 8:59 pace → 8:59 × 26.2 = 3:55:02
- Negative split (recommended): First 13 miles at 9:10, last 13 at 8:48
- 10% rule: Don’t go out faster than 10% slower than goal pace in miles 1–6
Factors that affect marathon performance:
- Temperature: Performance degrades ~1.5–3% for every 10°F above 55°F (13°C). Ideal marathon temperature: 44–54°F (7–12°C).
- Elevation gain: Each 1,000 feet of cumulative gain adds ~2–3 minutes.
- Fueling: Glycogen depletion (“hitting the wall”) at mile 18–22 is the biggest predictor of finish time deterioration. Consume 30–60g of carbohydrates per hour from mile 6 onward.
- Training: The formula assumes adequate training (peak week of 40–50+ miles).