Work out your running pace, finish time or distance in kilometres or miles, predict your 5K, 10K, half marathon and marathon times from a recent race, and get easy, steady, threshold and interval training paces you can use this week.
1. Pace, time or distance
Fill in any two and choose what to calculate.
Times at this pace
| Distance | Time |
|---|
Split times
| Km | Split | Total time |
|---|
2. Race predictor and training paces
Enter a recent race or all-out time trial (ideally in the last 6 to 8 weeks).
Predicted race times
| Race | Time | Per km | Per mile |
|---|
Your training paces
How this running pace calculator works
Pace is simply time divided by distance, so if you know any two of distance, time and pace, the third follows. The calculator shows your pace per kilometre and per mile, your speed in km/h and mph, the time you would reach common distances at the same pace, and a split table you can copy to your watch or write on your wrist. One mile is 1.609 km, a half marathon is 21.0975 km (13.1 miles) and a marathon is 42.195 km (26.2 miles).
How the race predictor works
The predictions use the endurance formula published by engineer and runner Peter Riegel: T2 = T1 × (D2 ÷ D1)1.06, where T1 and D1 are your recent race time and distance and D2 is the distance you want to predict. The exponent above 1 captures the fact that you slow down a little as races get longer. Riegel built his equation on world and age-group records lasting roughly 3.5 to 230 minutes, so it works best between those limits. In his 1981 paper the exponent for open world records was close to 1.08, but for men aged 40 to 70 it came out at 1.05 to 1.06, which is why 1.06 is a sensible choice for runners in their 40s and 50s.
The prediction assumes you are trained for the longer distance. A fast 5K tells you what your engine can do, not whether your legs and fuelling are ready for 42 km. A study of more than 2,000 recreational runners found Riegel’s formula was reasonably accurate up to the half marathon but clearly too optimistic for the marathon, especially for people running modest weekly distances. Treat the half and full marathon numbers as best-case targets that need consistent long runs to back them up.
This calculator does not age-grade your result. Age grading needs the full published age-factor tables for every distance and age, and we would rather leave it out than give you a rough version.
How your training paces are worked out
Your predicted 5K and 10K times are converted into an aerobic fitness score using the oxygen-cost equations of Jack Daniels and Jimmy Gilbert (the basis of the well-known VDOT tables). Each training zone is then set as a percentage of that score, following the intensity ranges in Daniels’ Running Formula: easy running at about 59 to 74 percent, steady (marathon-type) running at 75 to 84 percent, threshold at 83 to 88 percent and intervals at 95 to 100 percent. The result is a range, not a single number, because heat, hills, sleep and stress all change how a pace feels.
- Easy / zone 2: most of your running. You can talk in full sentences. If you can’t, slow down, even if the watch says you are inside the range.
- Steady: comfortable but purposeful. You can still speak in short sentences.
- Threshold: “comfortably hard”, about the effort you could race for an hour. You can only get out a few words at a time. Use 2 to 4 blocks of 6 to 10 minutes with short jog breaks.
- Intervals: hard. Talking is not an option. Use 3 to 5 minute repeats with equal or slightly shorter easy jogs.
The talk test is your built-in check. Being able to talk comfortably keeps you below your first breathing threshold (easy running); when speech becomes broken you are near that threshold; when you can no longer talk you are above the second one (threshold and harder). Research on well-trained endurance athletes shows most of them do roughly 80 percent of their sessions at low intensity, so keep the hard days few and the easy days truly easy. If you prefer heart rate, use the Zone 2 heart rate calculator and read our guide to zone 2 training. On hot or long runs, plan your fluids with the hydration calculator.
New to running or coming back after years off? Start with our Couch to 5K after 40 plan, then come back here to set your paces. For the bigger picture on fitness and ageing, see why VO2 max matters after 35.
Sources
- Riegel PS (1981). Athletic records and human endurance. American Scientist 69(3): 285–290
- Vickers AJ, Vertosick EA (2016). An empirical study of race times in recreational endurance runners. BMC Sports Science, Medicine and Rehabilitation 8: 26
- Daniels J. Daniels’ Running Formula (Human Kinetics), training intensities; oxygen-cost equations from Daniels J, Gilbert J (1979), Oxygen Power
- Bok D, Rakovac M, Foster C (2022). An examination and critique of subjective methods to determine exercise intensity: the talk test, feeling scale and rating of perceived exertion. Sports Medicine 52: 2085–2109
- Seiler S (2010). What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance 5(3): 276–291
This calculator gives general education, not medical advice. Predictions are estimates. If you have a heart condition, high blood pressure, diabetes, a recent injury or take medication that affects your heart rate, check with your doctor before hard training or racing.
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