Tool
Inputs → outputs
This page is intentionally practical: get numbers first, then read the how-to.
Inputs
- • Known distance (5K/10K/HM/Marathon)
- • Known time (hh:mm:ss)
- • Fatigue factor (exponent) (optional)
Outputs
- • Predicted times table
- • Predicted paces (per km/mile)
Examples
Calculator
Race time predictor (Riegel model)
Start with one recent performance, then estimate equivalent 5K / 10K / half marathon / marathon times. Useful for goal-setting and workout planning.
Default 1.06. Higher = more slowdown as distance increases.
Known result
Predicted half
A good checkpoint for endurance readiness.
Predicted marathon
Assumes you train the endurance + fueling required.
| Distance | Predicted time | Pace / km | Pace / mile |
|---|---|---|---|
| 5K | 23:59 | 4:48 | 7:43 |
| 10K | 50:00 | 5:00 | 8:03 |
| Half marathon | 1:50:19 | 5:14 | 8:25 |
| Marathon | 3:50:01 | 5:27 | 8:46 |
This is a simplified model. It does not account for heat, hills, fueling, or whether you’ve trained the durability needed for longer races. Use it for planning — then execute by effort.
Assumptions
What this tool assumes
- • Your known result reflects current fitness (recent and executed well).
- • Conditions and course difficulty are broadly comparable across distances.
Limitations
What can break it
- • Longer races require durability + fueling; many runners slow more than the model predicts without specific training.
- • Does not adjust for heat, hills, wind, altitude, or course difficulty.
Related
Use this with a plan
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FAQs
What is the fatigue factor (exponent)?
It controls how much the model expects you to slow as distance increases. Higher values predict more slowdown; the default is a common baseline.
Is this accurate for first-time marathoners?
Treat it as a rough estimate. First marathons are often limited by durability and fueling, not raw speed — execute a plan and practice fueling.
How should I use this for pacing?
Use it to set a realistic goal range, then pace by effort on race day and adjust for heat/hills. Don’t chase perfect splits in bad conditions.
Keep going
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