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Race Time Predictor

Enter one recent race and see predicted times for the mile, 5K, 10K, half and marathon with two methods side by side. A 10K in 50:00 predicts a 3:50:01 marathon with the Riegel formula and 3:49:34 with Daniels VDOT. Predictions assume you have trained for the distance.

h:mm:ss or mm:ss

Predicted times from 10K in 50:00 (VDOT 40.0)
RaceRiegel (1.06)Daniels VDOT
1 mile7:134:29 /km · 7:13 /mi7:074:25 /km · 7:07 /mi
5K23:594:48 /km · 7:43 /mi24:064:49 /km · 7:45 /mi
10K50:005:00 /km · 8:03 /mi50:005:00 /km · 8:03 /mi
Half marathon1:50:195:14 /km · 8:25 /mi1:50:525:15 /km · 8:27 /mi
Marathon3:50:015:27 /km · 8:46 /mi3:49:345:26 /km · 8:45 /mi
Predictions assume you have trained for the distance. The marathon is often slower than predicted for runners with low weekly mileage. Want to estimate your VO2max with a field test? Try the calculator on vo2max.io.

Formula used

Riegel (1981): T2 = T1 × (D2 ÷ D1)^1.06

Riegel’s paper fitted 1.05 to 1.06 for men aged 40 to 70 and 1.08 for world-class runners, over 1.5 to 42.2 km. We use 1.06. Check: 5K in 20:00 → half marathon 1:32:00.

Daniels and Gilbert (1979): we find your VDOT from the race (see the VDOT calculator for the equations) and then search for the time at each other distance that gives the same VDOT.

Worked example

10K in 50:00 to marathon with Riegel: 42.195 ÷ 10 = 4.2195. 4.2195^1.06 = 4.600. 50:00 × 4.600 = 3:50:01. Daniels VDOT for the same 10K is 40.0, which matches a half in 1:50:52 and a marathon in 3:49:34.

Ready to train for it? Use the beginner half marathon plan or the beginner marathon plan.

Questions and answers

How accurate are race time predictions?

They are a good guide if you have trained for the longer race. Many runners with low weekly mileage run the marathon slower than predicted, so treat the marathon figure as a best case.

What is the Riegel formula?

T2 = T1 × (D2 ÷ D1)^1.06. Peter Riegel described this power law in American Scientist in 1981. In his paper, records of men aged 40 to 70 fitted a “fatigue factor” of 1.05 to 1.06 and world-class runners 1.08.

What marathon time does a 50:00 10K predict?

Riegel gives 3:50:01. The Daniels VDOT method gives 3:49:34.

Why do the two methods differ?

They are built differently. Riegel is one power law fitted to records. Daniels and Gilbert model the oxygen cost of running and how long you can hold a share of your maximum. Showing both gives you a range.

Which distances can I enter?

Races from about 1.5 km to the marathon. That is the range Riegel used to fit his running data.

Sources

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