A simple formula helps runners estimate their marathon time using their 10K personal record, though coaches say it has limits.
The method, created by British running coach Frank Horwill, calculates marathon time as five times a 10K PR, minus 10 minutes. A 40-minute 10K, for instance, would suggest a 3:10 marathon.
How the formula works—and where it falls short
Tom Craggs, a UK-based coach and England Athletics’ national endurance manager, describes the formula as a useful guide but notes it’s only a starting point. “If you begin marathon training in great 10K shape, you have an excellent foundation,” he said. “But specific training for the marathon’s demands remains essential.”
Jo Wilkinson, a former elite marathoner and coach, believes half-marathon times predict performance more accurately. “Any race distance can estimate marathon performance, but accuracy improves the closer the distance is to 26.2 miles,” she said. Wilkinson still admits the 10K formula provides a reasonable indication of potential.
Its accuracy depends on the 10K time being run at race-day effort and within the same training cycle. She adds that marathon success involves more than speed—consistent training volume, pacing strategy, and practiced race nutrition all matter. “Poor pacing or fueling can ruin a marathon, even for well-prepared runners,” Wilkinson said.
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What the numbers show
The table below lists estimated marathon times based on 10K PRs, using Horwill’s method. A 32-minute 10K suggests a 2:30 marathon, while a 50-minute 10K points to a 4-hour finish. The estimates extend to an 8-hour marathon for runners with a 98-minute 10K.
- 32 mins → 2:30
- 34 mins → 2:40
- 36 mins → 2:50
- 38 mins → 3:00
- 40 mins → 3:10
- 42 mins → 3:20
- 44 mins → 3:30
- 46 mins → 3:40
- 48 mins → 3:50
- 50 mins → 4:00
- 52 mins → 4:10
- 54 mins → 4:20
- 56 mins → 4:30
- 58 mins → 4:40
- 60 mins → 4:50
- 62 mins → 5:00
- 64 mins → 5:10
- 66 mins → 5:20
- 68 mins → 5:30
- 70 mins → 5:40
- 72 mins → 5:50
- 74 mins → 6:00
- 76 mins → 6:10
- 78 mins → 6:20
- 80 mins → 6:30
- 82 mins → 6:40
- 84 mins → 6:50
- 86 mins → 7:00
- 88 mins → 7:10
- 90 mins → 7:20
- 92 mins → 7:30
- 94 mins → 7:40
- 96 mins → 7:50
- 98 mins → 8:00
Most runners view these estimates as rough benchmarks. The formula’s simplicity overlooks factors like course elevation, weather, and individual physiology. A runner’s ability to sustain effort over 26.2 miles often doesn’t follow neat predictions.
For those preparing for a marathon debut or aiming for a new personal best, the 10K-based formula gives a clear target. It shows how speed at shorter distances can support endurance—if training matches the goal.
Proper pacing is key to avoiding early fatigue.
Runners looking to refine their approach may find additional guidance in proven pace tips to start strong.
