Race Predictor Calculator
Predict your future 5K, 10K, Half Marathon, and Full Marathon finish times from a recent baseline race result.
Predict Race Performance (T_2 = T_1 · (d_2 / d_1)^1.06)
Enter your physical parameters below to compute verified race prediction metrics.
Calculation Results
Calculated using verified physical methodology: Riegel Race Predictor: T_2 = T_1 \times \left(\frac{d_2}{d_1}\right)^{1.06}
\text{Fatigue Exponent: } 1.06
Quick Summary
The Race Predictor Calculator estimates future race finish times across 5K, 10K, Half Marathon, and Full Marathon distances ($T_2 = T_1 \cdot (d_2 / d_1)^{1.06}$) using Peter Riegel's endurance scaling equation.
Formula Explanation
Riegel Race Predictor: T_2 = T_1 \times \left(\frac{d_2}{d_1}\right)^{1.06}
\text{Fatigue Exponent: } 1.06
How It Works
The Race Predictor Calculator converts baseline race time to total seconds ($T_1$). For any target distance ($d_2$), it computes the distance ratio ($d_2 / d_1$) and raises it to Peter Riegel's fatigue exponent ($1.06$). It predicts finish times for 5K, 10K, Half Marathon, and Full Marathon.
Step-by-Step Worked Example
Practical Problem: A runner has a recent $10.0\text{ km}$ race result of $50\text{ minutes } 00\text{ seconds}$ ($3,000\text{ seconds}$). Predict their finish times for 5K, Half Marathon, and Full Marathon.
- Step 1: Identify Baseline Parameters: $d_1 = 10.0\text{ km}$, $T_1 = 3,000\text{ seconds}$.
- Step 2: Predict 5K Finish Time ($d_2 = 5.0\text{ km}$): $T_{\text{5K}} = 3000 \times \left(\frac{5.0}{10.0}\right)^{1.06} = 3000 \times 0.47898 = 1,436.9\text{ s} = \mathbf{23\text{ min } 57\text{ sec}}$.
- Step 3: Predict Half Marathon Finish Time ($d_2 = 21.0975\text{ km}$): $T_{\text{Half}} = 3000 \times \left(\frac{21.0975}{10.0}\right)^{1.06} = 3000 \times 2.2136 = 6,640.8\text{ s} = \mathbf{01\text{ hr } 50\text{ min } 41\text{ sec}}$.
- Step 4: Predict Full Marathon Finish Time ($d_2 = 42.195\text{ km}$): $T_{\text{Full}} = 3000 \times \left(\frac{42.195}{10.0}\right)^{1.06} = 3000 \times 4.5682 = 13,704.5\text{ s} = \mathbf{03\text{ hr } 48\text{ min } 25\text{ sec}}$.
- Step 5: Review Target Pace: Marathon pace target = **5:25 /km** (**8:43 /mile**).
Real-World Calculation Examples
Scenario 1: From 5K Result (20m 00s 5K)
Parameters: $d_1 = 5.0\text{ km}$, $T_1 = 20\text{m } 00\text{s}$
Result: 10K = **41:45**; Half = **01:32:38**; Marathon = **03:10:48**. 5K baseline predictions.
Scenario 2: From 10K Result (50m 00s 10K)
Parameters: $d_1 = 10.0\text{ km}$, $T_1 = 50\text{m } 00\text{s}$
Result: 5K = **23:57**; Half = **01:50:41**; Marathon = **03:48:25**. 10K baseline predictions.
Scenario 3: From Half Marathon Result (1h 45m Half)
Parameters: $d_1 = 21.0975\text{ km}$, $T_1 = 1\text{h } 45\text{m } 00\text{s}$
Result: 5K = **22:40**; 10K = **47:26**; Marathon = **03:38:55**. Half marathon predictions.
Scenario 4: From Full Marathon Result (3h 30m Marathon)
Parameters: $d_1 = 42.195\text{ km}$, $T_1 = 3\text{h } 30\text{m } 00\text{s}$
Result: 5K = **21:44**; 10K = **45:24**; Half = **01:40:43**. Full marathon predictions.
Key Benefits of Using This Calculator
Peter Riegel Industry Standard
Uses Peter Riegel's 1.06 exponent model trusted by Runner's World and elite marathon programs.
Multi-Distance Race Matrix
Predicts 5K, 10K, 10 Mile, Half Marathon, and Full Marathon times simultaneously from 1 input.
Multi-Unit Readouts
Outputs predicted finish times, pace per km, pace per mile, and speed in km/h & mph.
100% Free & Client-Side
Executes locally in your browser with zero latency or web server transmission.
Frequently Asked Questions (FAQ)
What is a race predictor calculator?
A race predictor uses a recent race time to estimate your performance potential across different racing distances using fatigue scaling formulas.
What is Riegel's race predictor formula?
T2 = T1 * (d2 / d1)^1.06, developed by American engineer Peter Riegel in 1977.
How accurate are race predictor calculators?
Riegel's formula is highly accurate provided the runner has completed adequate weekly volume training for the target distance (e.g. 50+ km/week for marathon).
Why might someone fail to hit their predicted marathon time?
Lack of long runs (over 30 km), inadequate carbohydrate fueling, running the first half too fast, or hot/humid weather conditions.
What is Cameron's formula vs Riegel's formula?
Cameron's formula uses variable non-linear exponents for short track sprints, while Riegel's 1.06 exponent is optimized for endurance events between 3.5 minutes and 4 hours.
Can a 5K time predict a marathon time?
Yes, but 10K or Half Marathon times provide more reliable predictions because their aerobic energy contributions closer match full marathon demands.
What marathon time does a 20-minute 5K predict?
A 20-minute 5K predicts approximately a 3:10:48 full marathon.
What marathon time does a 40-minute 10K predict?
A 40-minute 10K predicts approximately a 3:02:44 full marathon.
What marathon time does a 1:45 half marathon predict?
A 1:45:00 half marathon predicts approximately a 3:38:55 full marathon.
How does course elevation change affect race predictions?
Every 100 meters of net elevation gain adds approximately 1.5 to 2.0 minutes to total marathon finish time.