What is calculated
A target-distance time from a known performance.
Race Time Predictor
Predicted target finish time
Enter your values, then calculate to see a verified result.
Reference range
How this result is calculated
A clear calculation path based on your inputs.
Inputs usedReview the information used for this result.
Full calculation and sourcesOpen Full calculation and sources to review normalized inputs, the formula sequence, assumptions, and evidence boundaries.
Versioned calculationFormula v1.0.0
Method
Apply the editable Riegel endurance exponent.
Important boundary
The model extrapolates one result and cannot establish readiness or safety.
Use a recent resultEnter distance and elapsed time from one representative effort.
5 km in 25:00Set the targetChoose the race distance to project.
10 kmKeep the exponentLabel any change from 1.06.
1.06 referenceInterpretation
is the modeled target finish time.
The fatigue penalty is shown separately from linear pace.
Treat large distance jumps with extra caution.
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Method and test recordFormula v1.0.0
- Recorded scope
- health-activity-performance-completion
- Publisher
- CalculatorGeek
- Recorded review date
- 2026-10-05
- Next source review
- 2027-04-05
- Definition fixtures
- 2 configured scenarios
- Published examples
- 2 shown below
Recorded method
Independently recompute the power model, unit equivalence, time formatting, and distance-boundary behavior.
These records describe the published model and reference tests. A test-case count is not a certification of every possible input or an independent specialist review. Editorial policy
Known limitations
- The model does not use training history, course, heat, altitude, wind, fueling, injury, or pacing execution.
- One exponent does not fit every athlete or distance pair.
- Large extrapolations have greater uncertainty.
- A predicted time is not a safe pacing prescription.
Method sources
Latest model update
2026-10-05 - Initial evidence-led shared-system implementation with fixtures, boundaries, original support content, and intentional cluster links.
Reference inputs and expected results
Up to 12 examples from the configured definition fixtures are shown. Expected values use the stated output units; invalid inputs are intended to be rejected.
| Case | Inputs | Expected result |
|---|---|---|
| five to ten kilometer projection | Known race distance: 5 km; Known race time: 25:00; Target race distance: 10 km; Endurance exponent: 1.06 count | Predicted target finish time: 3127.3972825; linear_seconds: 3000 (allowed numeric tolerance: 0.001) |
| same distance identity | Known race distance: 10 km; Known race time: 50:00; Target race distance: 10 km; Endurance exponent: 1.06 count | Predicted target finish time: 3000; Modeled fatigue above linear pace: 0 (allowed numeric tolerance: 0.0001) |
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On this page
What the Race Time Predictor answers
Project a target race time from a known race performance using the visible Riegel endurance model.
The calculator shows the distance ratio, predicted pace, and additional modeled fatigue instead of only a finish time.
Use the Sports calculators hub to choose the neighboring workflow rather than forcing one result to answer a different question.
How to use the Race Time Predictor
- Enter a recent known distance and time.
- Enter the target distance in the same or another supported unit.
- Keep 1.06 unless using a documented personal exponent.
- Use the result as a scenario beside course and training evidence.
Continue with the Pace Calculator. Inspect the exact distance-time ratio.
Formula, variables and calculation order
T2 = T1 x (D2 / D1)^1.06 by default. The editable exponent controls how rapidly pace slows as distance increases.
Inputs are normalized to the displayed base units, the calculation keeps full precision, and rounding is applied only to visible outputs.
Cross-check the next part of the workflow with the Running Race Planner. Turn a target into checkpoints and stopped-time handling.
Worked example and boundary check
Worked example
A 25:00 5K projected to 10K at exponent 1.06 gives about 52:04 rather than the linear 50:00.
Boundary check
Projecting from a sprint to a marathon, or from a stale/non-representative result, can produce a precise but unhelpful number.
How to interpret the result
The estimate is most useful when the known and target events are reasonably close and the known effort reflects current fitness.
- The model does not use training history, course, heat, altitude, wind, fueling, injury, or pacing execution.
- One exponent does not fit every athlete or distance pair.
- Large extrapolations have greater uncertainty.
- A predicted time is not a safe pacing prescription.
For a separate result with different assumptions, open the VDOT Calculator. Compare a second published performance model.
Frequently asked questions
What is the Riegel exponent?
It controls the modeled slowdown as distance rises; 1.06 is a common reference.
Should I change the exponent?
Only when you have enough comparable performances to justify a personal value.
Can I predict a marathon from a 5K?
The arithmetic works, but the large extrapolation may be poor because endurance specificity and fueling matter.
Why is the result slower than doubling my time?
The exponent adds a fatigue term when the target distance is longer.
Primary sources and evidence limits
Sources were checked 2026-10-05. They establish the stated method or interpretation boundary; they do not make a field estimate equivalent to laboratory measurement, coaching, medical diagnosis, or an individualized safety decision.