Running Pace Guide
How to Use a Negative Split in a Marathon
A negative split means running your second half faster than your first. Sounds obvious. Almost nobody does it. This guide gives you the actual pacing plan, the discipline it takes, and why it's the best way to stop blowing up after km 30.
To run a 4:00:00 marathon, you need to average:
Pace per km
5:41 /km
Pace per mile
9:09 /mi
Split Table
Use these checkpoints to stay on pace without obsessing over every single kilometre.
| Checkpoint | Target time |
|---|---|
| 5 km | 0:28:26 |
| 10 km | 0:56:53 |
| 15 km | 1:25:19 |
| 20 km | 1:53:45 |
| Halfway | 2:00:00 |
| 25 km | 2:22:12 |
| 30 km | 2:50:38 |
| 35 km | 3:19:05 |
| 40 km | 3:47:31 |
| 42.195 km | 4:00:00 |
Best pacing strategy
Don't think of it as first-half vs second-half. Use a gradual build: start 8–10 sec/km slower than goal pace in the first 5km, then shave 2–3 sec/km off every 5km block through the back half. This protects your glycogen, avoids early lactate buildup, and leaves you with a real window to accelerate after km 30 when everyone else is hanging on. For a 4:00 goal, target something close to a 2:02 / 1:58 split — not a 1:50 / 2:10 disaster in reverse.
Common mistakes
- Running goal pace in miles 1–3 because it 'feels easy' — it's supposed to feel easy, that's the plan working.
- Treating the half marathon marker as the signal to race. The real race starts at km 30.
- Skipping gels early because you feel great — the negative split falls apart if you hit the wall unfueled after km 35.
- Going so conservative in the first half that catching up becomes mathematically impossible.
- Never practicing progressive long runs in training, then expecting it to work on race day.
- Running by feel in the first-mile chaos instead of watching your GPS.
Race context
Boston: The downhill start tricks runners into going 20–30 sec/km too fast. A Boston negative split means actively braking on the Hopkinton descent.
Chicago / Berlin / London: Flat and fast — ideal for a textbook negative split. Terrain is removed as a variable, so pacing discipline is the whole game.
Hot weather: Tighten your target to a 2–3 min differential instead of 4–5. Never skip a water stop before km 25.
Large-field races: Seed one corral back if your plan is a conservative start. Getting swept up by faster runners in mile one is how negative splits die.
Hilly or coastal courses: Headwinds in the back half may mean a 1–2 min negative split is the best you'll get — and that's still a win.
FAQ
What is a negative split in a marathon?
Running the second half faster than the first. For a 4:00 goal, that's roughly 2:02 / 1:58. It's the most common pattern among runners who PB, and the least common among runners who fall apart after km 30.
How much slower should my first half be than my second?
For most runners, 2–5 minutes is realistic. A 2-minute differential (2:01 / 1:59) is modest and very doable. More than 6 minutes usually means the first half was too slow to be useful. Elites typically split within 60–90 seconds of each other.
Is a negative split better than an even split?
Both work. Negative splits tend to produce stronger finishes because they account for what glycogen depletion actually does to you after km 30. Even splits are harder to execute perfectly. For most runners chasing a PR, a small negative differential beats a perfect even split that unravels in the last 8km.
Can beginners run a negative split marathon?
Yes — and honestly the strategy is simpler for beginners: don't go out too hard. The hard part is mental. Holding back at km 5 when you feel great goes against every instinct. A GPS watch with pace alerts or a pace band on your wrist helps more than willpower alone.
When should I start fueling to support a negative split?
First gel at km 16–20, whether you feel like you need it or not. The back-half push needs energy that won't exist if you're glycogen-depleted by km 35. Fuel every 45–60 minutes and use the exact same nutrition you trained with.
What pace should I run the first half of a marathon for a negative split?
8–10 sec/km slower than goal average for the first 5–10km. Gradually come down to goal pace by km 15, then start your build. For a 4:00 marathon (5:41/km average), that means opening at around 5:50–5:52/km — not 5:20 just because it feels fine.
How do I practice negative splits in training?
Progressive long runs. Run the first half easy, close the final 8–10km at marathon pace or a touch faster. It trains your body to accelerate on tired legs — which is exactly what a negative split asks of you on race day.