Quick answer: even splits = goal time x split length / race distance. A 50:00 10K is 5:00 for every kilometre. With a 1% negative split the first half takes 25:15 and the second 24:45, so you open at about 5:05 per km and close at about 4:55.
How to use the split calculator
Choose a race or type any distance in km, miles or metres. Enter your goal time, then a split length: 1 km, 1 mile, 400 m or anything else. The last setting is the plan. Even splits keep the same pace from start to finish. A negative split makes the second half faster by the share of the finish time you choose; a positive split does the reverse. The finish time never changes. Print the table or download it as a CSV for a spreadsheet or a watch workout.
Worked example: a 1% negative split
Goal: 10K in 50:00 (3,000 seconds). 1% of 3,000 is 30 seconds, so the second half must be 30 seconds quicker than the first: 1,515 seconds (25:15) and 1,485 seconds (24:45). The tool spreads that change evenly, so pace drops a little every metre. The first kilometre comes out at 5:05.4, the fifth at 5:00.6, the sixth at 4:59.4 and the last at 4:54.6.
The same 2% plan on a 4:30:00 marathon gives halves of 2:17:42 and 2:12:18, a first mile of about 10:42 and a last full mile of about 9:55, against 10:18 for even pace.
How the negative split is modelled
Pace changes in a straight line over the distance, from slowest at the start to fastest at the finish (or the opposite for a positive split). That gives a smooth progression instead of two blocks, which is closer to how a controlled race feels. Real courses add hills, wind and water stops, so treat any single split as a guide and check yourself at the bigger checkpoints.
Choosing a percentage
Smaller is safer. One or two percent already means starting several seconds per mile slower than average, which is enough for most runners to feel in control early. Large negative splits are hard to execute and usually mean the first half was simply too slow.
Want the same splits on a wristband? Print a pace band. For checkpoints at round goal times use the marathon pace chart, and for lap times on a track use the track split calculator.
Formula and examples checked . Found a problem? Tell us.
Questions
What is a negative split?
Running the second half of a race faster than the first. On a 50:00 10K, a 1% negative split is a 25:15 first half and a 24:45 second half.
How do I calculate even splits?
Divide the goal time by the number of splits. A 2:00:00 half marathon is 13.11 miles, so each mile is 7,200 / 13.1094 = 549 seconds, or 9:09.
Is a negative split better than even pace?
Both work if the effort is controlled. The main benefit of planning a small negative split is that it stops you starting too fast, which is the most common pacing mistake.
Can I use split lengths other than a mile or a km?
Yes. Type any length, for example 400 m for track laps or 5 km for marathon checkpoints, and choose the unit next to it.