Race Shape › Calculators › Race time predictor
CalculatorRace time predictor
Put in one recent race — a parkrun is perfect — and get a predicted time for every distance up to the marathon, plus Two Oceans and Comrades. The model is Jack Daniels’ VDOT, the same one that sets every pace in a Race Shape plan.
| Distance | Predicted time | Pace |
|---|---|---|
| 5 km | 25:00 | 5:00/km |
| 10 km | 51:53 | 5:11/km |
| 15 km | 1:19:56 | 5:20/km |
| Half marathon | 1:55:03 | 5:27/km |
| Marathon | 3:57:55 | 5:38/km |
| Two Oceans 56 km * | 5:37:57 | 6:02/km |
| Comrades (about 90 km) * | 10:08:39 | 6:46/km |
Flat course, good conditions, properly trained for the distance. * Past the marathon, times follow how real Two Oceans and Comrades fields finish (about 1.42× and 2.56× a marathon), not the pure fitness model.
How the prediction works
Two curves do the work. One says how much oxygen it costs to run at a given speed; the other says what fraction of your maximum you can sustain for a given length of time. Put a real race through both and out comes one fitness number, VDOT, that predicts the others. A 25-minute 5 km is a VDOT of about 38 and points to a half marathon around 1:55 and a marathon around 3:58.
It is most accurate close to the race you entered and loosest far from it. A 5 km predicts a 10 km well and a marathon less well, because a marathon also tests endurance, fuelling and pacing that a 5 km does not. The prediction assumes you have trained for the longer race — it tells you what your fitness is worth, not what you will run on a 25 km-a-week build.
Beyond the marathon
Daniels’ model was built for 1.5 km to the marathon. Stretched further it is badly optimistic: it would put Comrades at about 2.15× your marathon, when real finishers average about 2.5×. So for Two Oceans and Comrades the predictor follows how real South African fields finish — about 1.42× a marathon for the 56 km and 2.56× for Comrades — and labels those rows. For your medal chances use the Comrades predictor or the Two Oceans predictor.
Use it to set paces, not just goals
The same number sets your training: easy runs, threshold and intervals all come off it. The training pace calculator shows them, corrected for the altitude you train at.
Race converters
- 5 km to half marathon converter
- 5 km to marathon converter
- 10 km to half marathon converter
- 10 km to marathon converter
- Half marathon to marathon converter
South African race predictors
- Soweto Marathon time predictor
- Two Oceans 21 km time predictor
- Cape Town Marathon time predictor
- Om Die Dam 50 km time predictor
- Midmar Mile time predictor
- Ironman 70.3 Durban time predictor
- Ironman South Africa time predictor
Common questions
How accurate is a race time predictor?
Within a few percent for nearby distances when you are trained for the race. Less so for the marathon off a 5 km, and only a rough guide past the marathon.
Which race should I enter?
A recent, all-out effort on a flat course: a parkrun, a 10 km or a half marathon. The closer it is to your goal distance, the better the prediction.
What is VDOT?
A single fitness number from Jack Daniels’ model. It behaves like VO₂max but comes from a race, so it includes how economically you run. More on VDOT.
Why is my marathon prediction faster than I ran?
Usually because the marathon needs endurance the shorter race does not test, or the first half went out too fast. Train the long run and pace the first half, and the gap closes.
Put this calculator on your club’s website
Free for running clubs, coaches, race organisers and bloggers. Copy the code below into any page that accepts HTML — WordPress, Wix and Squarespace all do — and your members get the same live race time predictor, with nothing to install and no sign-up.
Keep the credit line under it, please: that is the only thing we ask in return.
Related
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