Negative split calculator
Choose a distance, goal time and strategy. You get every split, the two halves, and a picture of how the plan spends your energy.
Strategy
Pace, split by split
Taller bar = slower split. You start conservatively and let the pace build as fatigue would normally slow you.
| Split | Split time | Pace /km | Elapsed |
|---|---|---|---|
| 1 km | 5:11 | 5:11 | 5:11 |
| 2 km | 5:08 | 5:08 | 10:19 |
| 3 km | 5:06 | 5:06 | 15:25 |
| 4 km | 5:04 | 5:04 | 20:29 |
| 5 km | 5:01 | 5:01 | 25:30 |
| 6 km | 4:59 | 4:59 | 30:29 |
| 7 km | 4:56 | 4:56 | 35:25 |
| 8 km | 4:54 | 4:54 | 40:19 |
| 9 km | 4:52 | 4:52 | 45:11 |
| 10 km | 4:49 | 4:49 | 50:00 |
Why negative splits work
Early in a race, adrenaline and fresh legs make goal pace feel easy, so it’s tempting to bank time. But the energy cost of running rises steeply with speed: 10 seconds per km too fast in the first half costs more than it saves, because you spend limited glycogen faster and accumulate fatigue that shows up as a slowdown later. Starting a few seconds per km slower than goal and finishing a few seconds faster spreads the effort more evenly.
This calculator ramps pace smoothly from the first split to the last, rather than jumping at halfway, which is closer to how a well-paced race feels. On hilly courses, pace for effort, not the clock. Check the goal itself with the race time predictor, and after the race, log your actual splits’ outcome in your running log.
Questions runners ask
What is a negative split in running?
Running the second half of a race faster than the first. A 50:00 10K split 25:30 then 24:30 is a negative split of one minute.
Is a negative split faster than even pacing?
For most runners, an even or slightly negative split gives the best time. Going out too fast burns carbohydrate and builds fatigue that costs more time late than it gained early. Most distance world records from 5,000 m to the marathon were run with even or slightly negative splits.
How big should my negative split be?
Small: 1–3% of your finish time. For a 4-hour marathon that’s a second half 2–7 minutes quicker than the first. Anything bigger usually means you started too slowly.
What is a positive split?
A second half slower than the first. It’s the most common pattern in marathons, where many runners start at goal pace or faster and fade after 30 km.