How the prediction works
A race time says two things about you: how fast you went, and how long you kept it up. Together they give one measure of your fitness. Two races that show the same fitness are equally good runs, so the calculator finds the time at each other distance that your fitness is worth.
It’s the same calculation the Strides app uses when you set your training paces from a race, so a time here matches what the app shows for the same race.
Race-day conditions adjust each equivalent without changing your underlying fitness. The adjustments are estimates; individual responses vary. The road animation illustrates climb and descent totals rather than an actual course profile.
Why your marathon might not match
An equivalent time assumes you’ve trained for that distance. Someone who runs a 22-minute 5K but has never gone further than eight miles won’t run the marathon it predicts. The shorter the race you enter and the longer the one you predict, the more the gap comes down to endurance rather than speed.
- Predictions are most reliable for distances close to your race: a 10K is a good guide to a half marathon, a 5K a weaker one to a marathon.
- Standard equivalents assume a flat course, cool weather, and rested legs. Use race-day conditions to explore a different course or forecast.
- They’re a ceiling on what your fitness allows today. Training is what closes the gap.
How Strides keeps it current
One race is a snapshot, and it gets older every week. Strides keeps your prediction up to date from every run, not just races. It reads your pace against your heart rate, allows for hills and heat, and shows a range rather than a single number. When your easy runs get faster at the same heart rate, your predicted times come down, before you’ve raced again.
Questions
How accurate is a race time predictor?
For a distance close to the race you entered, usually within a minute or two, if you’ve trained for it and race in good conditions. The further apart the two distances, the more the answer depends on training rather than fitness: a 5K time says a lot about your 10K and much less about your marathon.
Can I use a parkrun or a time trial?
Yes, if you ran it as hard as you could. A parkrun is an accurate 5K. A hard training run isn’t a race effort, so it will predict times slower than you can really run.
Why is the mile an input but not a prediction?
A mile result tells you a lot about your aerobic fitness, so it’s a good race to start from. Predicting a mile is less honest: it depends on speed and power that distance training doesn’t show, so the Strides app doesn’t predict it either.
Sources: Daniels, J. and Gilbert, J. (1979), Oxygen Power: Performance Tables for Distance Runners. Daniels, J., Daniels’ Running Formula, Human Kinetics.