What is a Negative Split?
A negative split means completing the second half of a race faster than the first. For a marathon, this means km 22–42 are run faster than km 1–21. Research consistently shows that negative-split runners experience less suffering, maintain better form, and finish faster than runners who go out hard and fade.
Why Negative Splits Work
Glycogen conservation: Starting slightly slower preserves muscle glycogen for the second half, reducing the risk of bonking (hitting the wall).
Aerobic efficiency: Early-race effort at slightly below threshold means you accumulate less lactate, keeping muscles functional longer.
Psychological advantage: Passing other runners in the second half — rather than being passed — provides a powerful mental boost.
The fastest marathon times in history were almost all run with negative or even splits. Eliud Kipchoge's sub-2-hour marathon attempt was run at perfectly even pace — the closest thing to optimal.
Negative Split Pace Plan — Marathon Example
If your goal marathon pace is 5:00/km (3:30:55 finish):
| Section | Distance | Target Pace | Section Time |
|---|---|---|---|
| First 5km | 0–5km | 5:08/km | 25:40 (conservative) |
| Building phase | 5–15km | 5:02/km | 50:20 |
| Goal pace | 15–30km | 5:00/km | 1:15:00 |
| Push phase | 30–38km | 4:58/km | 39:44 |
| Final sprint | 38–42.2km | 4:50/km | 20:20 |
Negative Split Targets for Common Races
| Race | Goal Time | First Half Pace | Second Half Pace |
|---|---|---|---|
| 10K | 40:00 | 4:03/km | 3:57/km |
| 10K | 50:00 | 5:03/km | 4:57/km |
| Half Marathon | 1:45:00 | 5:02/km | 4:56/km |
| Half Marathon | 2:00:00 | 5:44/km | 5:38/km |
| Marathon | 3:30:00 | 5:03/km | 4:57/km |
| Marathon | 4:00:00 | 5:44/km | 5:38/km |
Frequently Asked Questions
How much faster should the second half be in a negative split?
For a well-executed negative split, the second half should be 1–3% faster than the first half. In a 4:00 marathon, this means a first half of ~2:02 and a second half of ~1:58. Going more than 5% faster in the second half suggests you started too conservatively.
Is it always better to run a negative split?
For most recreational runners and most race distances, yes. Even splits are also excellent. The key is avoiding a positive split (second half slower) — which almost always indicates you went out too fast.
How do I practice negative splits?
Run your long runs with the first half at Zone 2 easy pace and the final 20–30% at marathon goal pace. This teaches your body the physiological and psychological pattern of building pace under fatigue.