Race predictor
One race in, four times out.
Put in a recent race and its time. The predictor works out what you could run at the other distances with the right training, and the paces to train at in minutes per kilometre.
Your recent race
Example: a 25:00 5k
From a 25:00 5k (5:00/km): the estimate
5k
25:00
5:00/km average
Your race10k
52:07
5:13/km average
Half marathon
1:55:00
5:27/km average
Marathon
3:59:47
5:41/km average
Training paces
| Run | Pace | What it is for |
|---|---|---|
| Easy | 6:15/km to 7:00/km | Most of your running. You can talk in full sentences. |
| Long run | 6:30/km to 7:15/km | The weekly long run; slower is fine. |
| Marathon pace | 5:41/km | Your predicted marathon pace; marathon-specific sessions. |
| Threshold | 5:20/km | Comfortably hard; roughly what you could hold for an hour. Tempo runs. |
| Intervals | 5:00/km | 5k pace, in repeats of 400m to 1km with jog recoveries. |
| Short reps | 4:45/km | Strides and 200m repeats; quick but relaxed. |
What the estimate assumes
- Riegel's formula: a time at a new distance equals your race time multiplied by (new distance ÷ race distance) to the power 1.06. It is the most widely used rule of thumb, from a 1977 study of race results.
- You train for the new distance. A marathon predicted from a 5k assumes the long runs a marathon needs; without them, expect five to ten per cent slower.
- A flat road course in decent weather, like the Porthcawl seafront. Hills, heat and wind all cost time.
- Training paces come from your predicted times: easy 125–140% and long runs 130–145% of 5k pace, threshold halfway between 10k and half-marathon pace, intervals at 5k pace, short reps at 95% of it.
- Times faster than 2:50 a kilometre or slower than 12:00 a kilometre are refused as probable typos or walking pace.
An estimate for planning, not a promise. Run by feel on the day, and stop if something hurts.
About the predictor
How accurate is the prediction?
For distances close to the one you raced, quite good. For a marathon from a 5k, often optimistic by five to ten per cent, because the marathon needs endurance the 5k does not test. Treat it as the best case after proper training.
Which race should I put in?
Your most recent all-out race or time trial, ideally from the last eight weeks, and ideally the distance closest to the one you are training for.
What are the training paces?
Easy and long runs well slower than race pace, threshold at roughly the pace you could hold for an hour, intervals at 5k pace, and short repetitions a little faster. They come from your predicted times, so they move as you improve.
Can I use it on hilly races?
Allow for the hills. The predictor assumes a flat road course like the Porthcawl seafront; a hilly half can be several minutes slower.
Your first club run is free. Tuesday, 6:30, the lighthouse.
Turn up five minutes early and find a coach in a teal jacket. There are four pace groups and a back marker who finishes last on purpose, so whatever your pace, you will not be running on your own.