Race time predictor
Enter a recent race and see what it says you can run from the mile to the marathon, with the training paces that get you there.
| Race | Time | Pace /km |
|---|
| Training pace | /km | /mile |
|---|
How it works
Your race is turned into a 5K at the same effort with Riegel's formula, and every other distance worked out from that, the same way Moonstride does from your Apple Watch runs. Past 30 km the formula allows a little more slowing, since the usual version promises most runners a marathon that's too quick.
A fast 5K doesn't mean you can hold that effort for 21 or 42 km until the long runs are there. Fill in your longest run and weekly distance and races past 10K slow down until your long run reaches three quarters of the race and you run one and a half races' worth a week.
Training paces come from your 5K pace: easy and long runs 27% slower, steady 15%, tempo 7%, intervals at it and strides a little quicker. They're for flat ground: the hill pace calculator shows how much to ease off on a climb.
Questions
How does the race time predictor work?
It uses Riegel's formula, which says how much slower the same effort is over a longer distance: a race twice as long takes a little over twice as long. It's the formula Moonstride uses, with one change: for the marathon it allows a little more slowing, because the usual formula promises most runners a marathon that's too quick.
What can I run with a 25 minute 5K?
About 52:07 for 10K, 1:55:00 for a half marathon and 4:10:14 for a marathon, if you've done the training for the longer distance.
How accurate is it?
Close for distances near the one you raced, if you've trained for them. It assumes you're as well prepared for the longer race as the shorter one, which is rarely true of a marathon. Fill in your longest recent run and weekly distance and it slows longer races until your training is there, as the app does.
Which race should I enter?
A recent one you ran all out, ideally from 5K to the half marathon, and the closer to your target distance the better. A parkrun works well. Anything shorter than a mile is too short to say much about longer races.
What are training paces?
The paces your week's runs should be at, worked out from your race: easy runs about a quarter slower than your 5K pace, tempo a little slower than it, and intervals at it. Most of your running should be easy.
Why is my marathon prediction slower than other calculators?
Most calculators use Riegel's formula as it is, which works well to the half but is usually too quick for the marathon. This one allows a little more slowing over the full distance, and more again if your long runs and weekly distance aren't there yet.
More free tools
- Route plannerDraw a run or get loops from your door, every hill coloured by gradient.
- Pace calculatorPace from a distance and time, a finish time from a pace, or how far you'll get.
- Hill pace calculatorHow much slower the same effort runs uphill, and how much quicker down.
- GPX viewerOpen a GPX file and see its distance, climbs and elevation profile.
Let it do the sums
Moonstride predicts your race times from every run you record with your Apple Watch, and builds the plan to race day around them, paces and all.
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