Negative Split Pacing | How to Calculate Your First-Half and Second-Half Times and Build the Plan
The best-known strategy for not fading in the second half of a marathon is the “negative split”: running the second half faster than the first. But “hold back early” does not tell you how much to hold back. This guide uses concrete numbers to explain the difference between negative and positive splits, what percentage gap to aim for between the halves, how to calculate each half for a sub-4 marathon, how to build a split table where the pace rises gradually, and which pacing suits a first-time marathoner.
What is a negative split? Running the second half faster than the first
A negative split is a pacing plan in which you run the second half of a race faster than the first. Subtracting the first-half time from the second-half time gives a negative number — hence “negative”. The opposite, where the second half is slower, is a positive split, and running both halves in the same time is even pacing.
| Pacing | Second half − first half | Characteristics |
|---|---|---|
| Negative split | Negative (second half faster) | Holding back early leaves energy for the second half. A common shape in elite record runs |
| Even pace | 0 | The same pace from start to finish. In theory, the most efficient |
| Positive split | Positive (second half slower) | Where most recreational runners end up. Time banked early is lost to the late slowdown |
In a marathon, running the first half too fast burns through your stored carbohydrate (glycogen) early, and your legs can suddenly stop cooperating after 30 km. A negative split — holding back a little early to keep something in reserve — is a way to prevent that collapse.
How big should the gap be? Aim for 1–2%
A negative split does not mean a big surge in the second half. The usual gap between halves is about 1–2% of your total time. For a runner finishing a marathon in around 4 hours, 1% is about 2 min 24 s and 2% about 4 min 48 s. Make the gap too large and the first half becomes so slow you cannot make it back.
| Pacing (net 3:55:00) | First half | Second half | Pace at the start | Pace near the finish |
|---|---|---|---|---|
| Negative 2% | 1:59:51 | 1:55:09 | 5:48 | 5:21 |
| Negative 1% | 1:58:41 | 1:56:19 | 5:41 | 5:27 |
| Even | 1:57:30 | 1:57:30 | 5:34 | 5:34 |
| Positive 1% | 1:56:20 | 1:58:41 | 5:27 | 5:41 |
| Positive 2% | 1:55:09 | 1:59:51 | 5:21 | 5:48 |
The table compares a plan to finish in 3:55 on your watch, changing only the pacing (paces are per kilometre). Even at negative 1%, the halves differ by 2 min 22 s, and the pace rises gradually from 5:41 per km just after the start to 5:27 per km near the finish.
How to calculate the first-half and second-half times
You can calculate the two halves from your goal time and the pacing percentage as follows. It is easiest to think of adding half the gap to the first half and subtracting half from the second.
You could split the race into just two paces, but a sudden pace change at halfway is hard on the body. The Marathon Pace Band Maker spreads the change so the pace shifts gradually in proportion to distance. If the second half minus the first half is d seconds and the running time excluding aid-station stops is T, the pace at point x is the average pace × (1 + 4d ÷ T × (x ÷ distance − 0.5)). The pace equals the average exactly at halfway, with the biggest difference at the start and finish.
| Segment (sub-4, negative 1%) | Elapsed time | Segment pace (per km) |
|---|---|---|
| 0–5 km | 28:56 | 5:47 |
| 5–10 km | 57:45 | 5:46 |
| 10–15 km | 1:26:25 | 5:44 |
| 15–20 km | 1:54:57 | 5:42 |
| 20–25 km | 2:23:21 | 5:41 |
| 25–30 km | 2:51:37 | 5:39 |
| 30–35 km | 3:19:44 | 5:38 |
| 35–40 km | 3:47:44 | 5:36 |
| 40 km–finish | 3:59:59 | 5:35 |
You only speed up by 1–2 seconds every 5 km, so to the runner it feels like “almost the same pace”. Even so, you reach halfway about a minute later than with even pacing, leaving your legs fresher for the second half.
Which pacing to choose: first marathon vs chasing a time
- First marathon: negative 1–2%. Hold back early and make not walking after 30 km your top priority
- Chasing a personal best: negative 1% or even. Confirm in long runs such as a 30 km session that you can hold the pace in the second half
- You always fade badly after 30 km: one option is to plan a positive 2–4% so your plan realistically counts on banking time early
- Hilly courses: you lose time on climbs and regain it on descents, so expect larger deviations in each 5 km segment
Planning a positive split “assumes you will slow down”, which can look defeatist. But for runners who really do slow down every time, the numbers on the pace band stay closer to reality, so they do not panic late in the race. The risk is that starting faster can make the slowdown even worse.
FAQ
- What is a negative split?
- A pacing plan where you run the second half of a race faster than the first. Second-half time minus first-half time is negative, hence the name. Holding back early leaves energy for the second half, which helps prevent the slowdown after 30 km in a marathon.
- How many minutes faster should the second half be in a negative split?
- About 1–2% of your total time. For a runner around 4 hours, 1% is about 2 min 24 s and 2% about 4 min 48 s. Make the gap too large and the first half gets so slow you cannot make it back.
- What first-half time should I run for a sub-4 with a negative split?
- At negative 1%, about 2:01:11 for the first half and about 1:58:48 for the second. Speed up gradually from around 5:48 per km just after the start to around 5:34 per km near the finish.
- Is a positive split a bad way to run?
- Not necessarily. If you build the expected late slowdown into your plan, the gap between your pace band and reality shrinks. But starting too fast makes the slowdown bigger, so keep the gap to 2–4%.
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