Make your next run count
Finish time predictor
Estimate finish times at other distances from a recent race result.
Enter the distance and time of a recent race to compare estimated 5K, 10K, half marathon and marathon finishes. The calculation allows for a slower average pace over longer distances. Use the results as a starting point for considering a goal; your preparation and race conditions can change the outcome.
You can enter your recent distance in kilometres or miles, and a prediction for that same distance returns your original time. Save a PDF or share your settings to keep the estimates for later comparison.
Estimated finish times
An endurance-model estimate for four race distances.
- 5K
- 23:59
- 10K
- 50:00
- Half marathon
- 1:50:19
- Marathon
- 3:50:01
An estimate from the Riegel formula, not a guarantee. Training, terrain, weather and pacing affect your actual result.
For general information only, not professional advice. Check the official sources below. Use your own judgement and speak to a qualified professional before you act.
A little context
Get more from your result.
The steps, examples and sources
behind this tool.
Estimate your next race time
- Enter your recent race distance in kilometres or miles.
- Enter its finish time as m:ss or h:mm:ss.
- Select Calculate estimate to see times for four race distances.
- Save a PDF, share your settings or print the estimate.
A worked example
- Recent 10K in 50:00.
- Estimated 5K: 23:59; half marathon: 1:50:19; marathon: 3:50:01.
How this tool works
The Riegel model is T2 = T1 x (D2 / D1)^1.06. Distances use the same unit; calculations preserve precision and displayed times round to the nearest second.
A target equal to your input distance returns the same time. Longer distances imply a slower average pace under this endurance model.
The estimate does not account for training, terrain, weather or individual endurance. It is not a guarantee or a training prescription.
A few useful answers
Sources
- American Scientist; Pete Riegel archive: Peter Riegel: Athletic Records and Human Endurance (1981)
Power-law relationship between event distance and time; this tool uses the specified endurance exponent 1.06.
- World Athletics: Competition and Technical Rules (2026 edition), Technical Rule 55.1
Technical Rule 55.1, PDF page 250: Road Mile 1609.344 m and Marathon 42.195 km. Half-marathon distance is confirmed by the separate discipline record.
- World Athletics: Marathon (discipline page)
Marathon distance: 26 miles 385 yards (42.195 km).
- World Athletics: Half marathon (discipline page)
Half marathon distance: 21.0975 km, exactly half a marathon.
- National Institute of Standards and Technology (NIST): NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically
One mile = 1609.344 metres (exact factor).
Last checked:
StrideSheet team
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