Running Time Predictor
Estimate your finish time, pace, and speed for any race distance using a recent performance. Built on the peer‑reviewed Riegel model and optimized for accuracy, accessibility, and speed.
Interactive Calculator
Results
Equivalent times across popular races
Based on your recent race and chosen exponent k.
| Distance | Predicted Time | Pace/km | Pace/mi |
|---|---|---|---|
| Enter your recent race to see equivalents. | |||
Data Source and Methodology
Authoritative Data Source: Peter S. Riegel (1981), “Athletic Records and Human Endurance,” American Scientist, 69(3), 285–290.
Stable reference: JSTOR 27850761. Access summary: https://sporttracks.mobi/labs/race-finish-time-predictor and the original publication where available.
All calculations are derived from the Riegel model: performance scales with distance by a power law using exponent k.
Read the American Scientist reference
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Riegel model:
$$ T_2 = T_1 \times \left(\frac{D_2}{D_1}\right)^k $$
Optional conditions adjustment:
$$ T_{2,adj} = T_2 \times \left(1 + \frac{A}{100}\right) $$
Pace and speed:
$$ \text{Pace}_{km} = \frac{T_{2,adj}}{D_2\,[km]} \quad;\quad \text{Speed}_{km/h} = \frac{D_2\,[km]}{T_{2,adj}\,[h]} $$
Glossary of Variables
- T1: Your recent race finish time.
- D1: Your recent race distance.
- D2: Your target race distance.
- k: The Riegel exponent (performance decay factor with distance).
- A: Conditions adjustment in percent (−20 to +20).
- T2: Predicted finish time for the target distance.
- T2,adj: Predicted time after applying conditions adjustment.
- Pace per km / mile: Average time to cover one kilometer / one mile.
- Speed: Average speed expressed in km/h and mph.
How It Works: A Step-by-Step Example
Come Funziona: Un Esempio Passo-Passo
Suppose your recent 10K time is T1 = 00:45:00 and you want to predict a half marathon (D2 = 21.0975 km), using k = 1.06.
Given:
D1 = 10 km
T1 = 45 min = 2700 s
D2 = 21.0975 km
k = 1.06
Compute:
$$ T_2 = 2700 \times \left(\frac{21.0975}{10}\right)^{1.06} \approx 5825\;s \approx 01:37:05 $$
Pace:
$$ \text{Pace}_{km} = \frac{5825}{21.0975} \approx 276\;s/km \approx 4:36/km $$
$$ \text{Pace}_{mi} \approx 7:24/mi $$
If race day is hot (+5%), apply A = +5:
$$ T_{2,adj} = 5825 \times \left(1 + \frac{5}{100}\right) \approx 6116\;s \approx 01:41:56 $$
Frequently Asked Questions (FAQ)
Which formula does this predictor use?
It uses the peer‑reviewed Riegel model: T2 = T1 × (D2/D1)^k. See Data Source and Methodology for the reference.
What exponent k should I choose?
Default to 1.06. Choose 1.03–1.05 if you have strong speed over short distances; choose 1.06–1.10 if you maintain performance well over longer distances.
How do weather and terrain affect predictions?
They can shift results by several percent. Use the Conditions Adjustment to reflect expected race-day factors.
Can I enter custom distances?
Yes. Select Custom for recent and/or target distance and choose your unit (km or miles).
Are the paces per km and per mile both shown?
Yes, results include pace per km and per mile, plus speed in km/h and mph.
Will taper or training changes impact accuracy?
Yes. The model assumes comparable fitness. If training volume or taper differs, consider a small negative or positive adjustment.
Last reviewed for accuracy on: September 14, 2025.