A good toolfor estimating a half-marathon time shouldn't promise a magical time.
Its purpose is more useful than that: it starts with a recent time run over a shorter distance, then adjusts that projection based on the factors that actually influence performance over 21.1 km.
To estimate your finishing time, you need to consider the race distance, your endurance level, your training volume, and your ability to maintain your pace as the race progresses.568
The calculator provided by Protéalpes is designed to convert actual time into estimated time, and then calculates your average pace, pace per kilometer, and split times. This allows you to set a realistic time goal, whether you’re simply running a half-marathon or aiming for a personal best.
Half-Marathon Time Calculator
Benchmark performance
For the freshness of the reference; if empty, a neutral assumption is used.
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What method should you use to estimate your half-marathon time?
The simplest and most reliable method is to use a recent race as a baseline —typically a 10K or another half marathon. The most commonly used model is Riegel’s formula:
T2 = T1 × (D2 / D1)^1.06
It allows you to estimate a time for one distance based on another. To convert from a 10K to a half-marathon, you generally multiply your 10K time by approximately 2.206. A runner who completed a 10K in 50 minutes can therefore estimate a half-marathon time of around 1 hour and 50 minutes.12
This foundation remains solid, as a study of more than 2,300 recreational runners showed that Riegel’s formula was generally accurate for distances up to a half-marathon, though it becomes significantly less reliable for predicting a full marathon. It is therefore an excellent starting point for estimating your time over 21.1 km.2
Refine the pace prediction calculation
In practice, a recent 10K time is often the best indicator of pace for a half marathon. That said, two runners with the same 10K time won’t always achieve the same result over 21.1 km. It all depends on their running style: whether they’re a runner with great endurance, a well-rounded runner, or, conversely, a runner who is faster than they are durable.
A runner with strong endurance, capable of sustaining their effort for a long time, will often perform better in a half marathon than in a 10K. Conversely, a runner with limited endurance may experience a more pronounced drop in speed in the final kilometers, even with a very high maximum aerobic speed.
That is why a good training plan should not only take into account a benchmark race, but also the athlete’s fitness level and endurance profile.56
When no recent time trial results are available, a field test can also be useful. Among recreational runners, the Cooper test has shown a good ability to predict half-marathon performance, sometimes outperforming certain variables derived from a laboratory test.
The VMA therefore remains useful, especially for creating a personalized training plan, but it is not always sufficient on its own to accurately estimate a half-marathon time.34
How do you calculate your average pace and split times?
Once you've estimated your half-marathon time, the calculation is simple:
average pace = target time / 21.0975 km
For example, for a goal of 1 hour 45 minutes, the target pace is about 4 minutes 59 seconds per kilometer. This is the basis for any pace calculator, any average speed calculation, and any split time calculation.
For example, this results in:
- 5 km: 24:53
- 10 km: 49:46
- 15 km: 1:14:39
- 20 km: 1:39:32
- Finish time: 1:45:00
You can also use a pace chart.
Table of pace and split times for the half marathon
| Allure | Speed | Level (marathon) | 1 km | 5 miles | 10 km | 15 km | 20 km | Semi |
|---|---|---|---|---|---|---|---|---|
| 3:00 a.m. | 20 | World Elite | 3:00 a.m. | 3:00 PM | 30:00:00 | 45:00:00 | 1:00 | 1:03:18 |
| 3:15 a.m. | 18,46 | National Elite | 3:15 a.m. | 4:15 PM | 32:30:00 | 48:45:00 | 1 hour and 5 minutes | 1:08:34 |
| 3:30 a.m. | 17,14 | Elite | 3:30 a.m. | 5:30 p.m. | 35:00:00 | 52:30:00 | 1 hour 10 minutes | 1 hour, 13 minutes, 50 seconds |
| 3:45 a.m. | 16 | Very good | 3:45 a.m. | 6:45 p.m. | 37:30:00 | 56:15:00 | 1 hour and 15 minutes | 1:19:07 |
| 4:00 a.m. | 15 | Under 2 hours 49 minutes | 4:00 a.m. | 8:00 p.m. | 40:00:00 | 1:00 | 1 hour 20 minutes | 1:24:23 |
| 4:15 a.m. | 14,12 | Under 3 hours | 4:15 a.m. | 9:15 PM | 42:30:00 | 1 hour 3 minutes 45 seconds | 1 hour 25 minutes | 1 hour 29 minutes 40 seconds |
| 4:30 a.m. | 13,33 | Under 3 hours and 10 minutes | 4:30 a.m. | 10:30 p.m. | 45:00:00 | 1 hour and 7 minutes and 30 seconds | 1 hour 30 minutes | 1 hour, 34 minutes, 56 seconds |
| 4:45 a.m. | 12,63 | Under 3 hours and 21 minutes | 4:45 a.m. | 11:45 p.m. | 47:30:00 | 1 hour 11 minutes 15 seconds | 1 hour and 35 minutes | 1 hour, 40 minutes, 13 seconds |
| 5:00 a.m. | 12 | Under 3 hours and 31 minutes | 5:00 a.m. | 25:00:00 | 50:00:00 | 1 hour and 15 minutes | 1 hour 40 minutes | 1 hour, 45 minutes, and 29 seconds |
| 5:15 a.m. | 11,43 | Under 3 hours 42 minutes | 5:15 a.m. | 26:15:00 | 52:30:00 | 1:18:45 | 1 hour 45 minutes | 1 hour 50 minutes and 46 seconds |
| 5:30 a.m. | 10,91 | Under 3 hours 52 minutes | 5:30 a.m. | 27:30:00 | 55:00:00 | 1 hour and 22 minutes and 30 seconds | 1 hour 50 minutes | 1:56:02 |
| 5:45 a.m. | 10,43 | Under 4:03 | 5:45 a.m. | 28:45:00 | 57:30:00 | 1 hour 26 minutes and 15 seconds | 1 hour 55 minutes | 2:01:19 |
| 6:00 a.m. | 10 | Under 4 hours and 13 minutes | 6:00 a.m. | 30:00:00 | 1:00 | 1 hour 30 minutes | 2:00 | 2:06:35 |
| 6:15 a.m. | 9,6 | Under 4 hours and 24 minutes | 6:15 a.m. | 31:15:00 | 1 hour and 2 minutes and 30 seconds | 1 hour, 33 minutes, 45 seconds | 2:05:00 | 2:11:52 |
| 6:30 a.m. | 9,23 | Under 4 hours and 35 minutes | 6:30 a.m. | 32:30:00 | 1 hour and 5 minutes | 1 hour, 37 minutes, and 30 seconds | 2 hours and 10 minutes | 2:17:08 |
| 6:45 a.m. | 8,89 | Under 4 hours and 45 minutes | 6:45 a.m. | 33:45:00 | 1 hour and 7 minutes and 30 seconds | 1 hour, 41 minutes, 15 seconds | 2 hours and 15 minutes | 2:22:24 |
| 7:00 a.m. | 8,57 | Under 4 hours and 56 minutes | 7:00 a.m. | 35:00:00 | 1 hour 10 minutes | 1 hour 45 minutes | 2 hours and 20 minutes | 2:27:41 |
| 7:15 a.m. | 8,28 | Under 5:07 | 7:15 a.m. | 36:15:00 | 1 hour and 12 minutes and 30 seconds | 1 hour 48 minutes and 45 seconds | 2 hours and 25 minutes | 2:32:57 |
| 7:30 a.m. | 8 | Sub 5:17 | 7:30 a.m. | 37:30:00 | 1 hour and 15 minutes | 1 hour 52 minutes 30 seconds | 2 hours and 30 minutes | 2:38:14 |
| 8:00 a.m. | 7,5 | Under 5:38 | 8:00 a.m. | 40:00:00 | 1 hour 20 minutes | 2:00 | 2 hours 40 minutes | 2:48:47 |
You can download this pace chart for free here.
This kind of benchmark is invaluable on race day because it helps prevent a common mistake: starting out too fast. In practice, many runners maintain a pace close to their target at the start of the race, only to lose momentum as the race progresses.
Studies on pacing also show that positive pacing is common: pace slows slightly as fatigue sets in.7
Training changes the estimate
Half-marathon times also depend heavily on training. A study of recreational runners showed that half-marathon times were linked in particular to VO2max, BMI, and weekly mileage.5
Another study found that higher training volume, longer long runs, and faster training pace were associated with better performance in the half marathon.6
This means that the same 10K time does not yield the same projection depending on the context. A consistent, well-prepared runner with a solid aerobic base will often be able to translate their performance better than a less-trained runner.
A good tool should go a step further than a simple rule of three: it should take into account not only the time spent but also the consistency of the profile.
Conclusion
This calculator serves three purposes: estimating your finish time, calculating your pace, and developing a consistent race strategy. It doesn’t replace experience, a coach, or a personalized training plan, but it helps you move from a vague idea to a realistic time goal.
So the best method is actually quite simple:
- Starting from a recent time stamp,
- use a Riegel projection,
- and then adjust it based on your stamina, consistency, and fitness level.
This is the most reliable wayto estimate a half-marathontime —no empty promises and no false miracles.
Scientific references and sources
2 An empirical study of race times among recreational endurance runners by Andrew J. Vickers et al.
3 The Cooper Test Provides a More Accurate Prediction of Half-Marathon Performance in Recreational Runners Than Laboratory Tests by José R. Alvero-Cruz et al.
4 A Simple Equation for Estimating Half-Marathon Race Times Based on the Cooper Test in Recreational Runners by José R. Alvero-Cruz et al.
5 Predictors of half-marathon performance in male recreational athletes by Pantelis T. Nikolaidis et al.
6 Training for a (half-)marathon: Training volume and longest endurance run in relation to performance and running injuries by Tjardo Fokkema et al.
7 Pacing Strategies for Women and Men in Half-Marathon and Marathon Races by Pantelis T. Nikolaidis et al.
8 Half Marathon | Copenhagen 26 by World Athletics
