Negative Split: How to Pace Your Race Effort
What a negative split is and how to pace your effort in a 5K, 10K, half marathon and marathon, with numeric examples and the math for your own goal.
In this article
A negative split is running the second half of a race faster than the first. It contrasts with a positive split, which is running the second half slower, and with even pacing, which holds the same pace from start to finish. Pacing well comes down to choosing one of those three profiles before the start and not letting your nerves choose it for you.
This article explains the three profiles, the general math for working out your two halves with any goal, numeric examples for a 5K, 10K, half marathon and marathon, and what happens if you go out too fast. The numbers are examples of our own design: they are guidance and should be adapted to your own result.
The three race profiles
- Even pace: the same pace in every kilometer. It is the easiest to follow with a watch.
- Negative split: the second half is faster. It requires starting with some restraint, so that the first kilometers feel easy.
- Positive split: the second half is slower. It usually happens without meaning to when you go out too fast.
A negative split does not mean starting slow or leaving time on the table: it means the difference between the two halves is small and in favor of the second. With a time goal, what counts is that the sum of the two halves gives your goal.
The math for any race
With two halves of the same distance, the math is simple:
- Work out your average pace by dividing the goal time by the kilometers.
- Choose a small difference, a few seconds per kilometer. We will call it d.
- First half: average pace plus d. Second half: average pace minus d.
- Multiply each pace by the kilometers in its half and add them up: it should give your goal.
The trick is that the average pace comes out exact because the two halves are the same length. If the first is 4 seconds slower than the average and the second 4 faster, they cancel out. In a half marathon, each half is 10.54875 km, and in a marathon, 21.0975 km.
Numeric examples
This table applies the math to four goals. Paces are rounded to the second.
| Goal | Average pace | First half | Second half | Difference per km |
|---|---|---|---|---|
| 5K in 25:00 | 5:00 | 12:40 (5:04 per km) | 12:20 (4:56 per km) | 8 seconds |
| 10K in 58:00 | 5:48 | 29:20 (5:52 per km) | 28:40 (5:44 per km) | 8 seconds |
| Half marathon in 1:55:00 | 5:27 | 58:00 (5:30 per km) | 57:00 (5:24 per km) | about 6 seconds |
| Marathon in 4:30:00 | 6:24 | 2:16:00 (6:27 per km) | 2:14:00 (6:21 per km) | about 6 seconds |
Notice that the difference between halves is small. In the 10K, the second half is 8 seconds per kilometer faster than the first, and the whole job is not spending too much early on.
What happens if you go out fast
Take the 10K in 58:00 (5:48 per kilometer). Imagine you run the first five kilometers at 5:30, which is 27:30. In the first half you have gained 90 seconds over even pace (18 seconds per kilometer for 5 kilometers).
To meet the goal, the second half has to be run in 30:30, which is 6:06 per kilometer. That is 18 seconds per kilometer slower than the average and 36 slower than the pace you started at. But if you cannot hold 6:06 and only manage 6:20, the second half takes 31:40 and you finish in 59:10, 70 seconds over the goal.
That is the trap of the positive split: the cushion from the first half is spent with interest in the second.
When it makes sense and when it does not
- With a time goal and a regular course, an even pace or a small negative split are reasonable options.
- If it is your first race at a distance and you do not know your pace, go by effort on a scale of 0 to 10: the first kilometers should feel clearly below what you will feel at the end.
- If there is a big crowd at the start, it is hard to hold the planned pace in the first minutes. Do not fight it: let it thin out and spread what is missing over the following kilometers.
- If your goal is just to finish, you do not need to work out halves: it is enough to start calmly and finish better than you started.
How to rehearse it in training
You do not have to find out in the race. You can rehearse the split in a race-pace block. With the 10K in 58:00, for example, a block of 6 kilometers split into two halves: 3 kilometers at 5:52 (17:36) and 3 kilometers at 5:44 (17:12). That is 34:48 in total, not counting the warm-up.
To see how a goal fits with a full strategy, look at how to run a 10K in 50 minutes and half marathon in 2 hours, which work out splits for other goals. If you want to know whether your goal is realistic before splitting it, there is the pace calculator and time predictor and predict your race time.
How to follow it in the race
- Pass the halfway point and compare with your planned time: in the example 10K, 29:20.
- Use the race markers for the halfway point. If your watch measures a slightly different distance, the official marker rules, and the reason is in why your GPS watch reads longer than the race.
- If you are behind, do not make it up all at once: spread the difference over the kilometers that remain.
- If you are ahead, hold steady. You do not need to bank more time.
- In the last stretch, give what is left if you feel strong.
Common mistakes
- Choosing a difference between halves that is too big.
- Going out fast in the first kilometers because of the excitement of the start.
- Treating the negative split as an obligation: it is an option, not a rule.
- Changing the split on race day without having tried it.
- Staring at your watch obsessively instead of checking it kilometer by kilometer.