A split is the time for one section of a race, usually a mile or a kilometer. This split calculator turns a goal finish time into a split plan: enter the distance and the time, choose even, negative or positive splits, and it lists the time for every mile or kilometer and the clock time you should see at each marker.
A negative split means running the second half faster than the first. You choose how much faster as a percentage: at 2%, each second-half mile takes 2% less time than a first-half mile, and the two halves still add up to your goal time. For a 3:30:00 marathon, a 2% negative split is 1:46:04 for the first half and 1:43:56 for the second, or 8:05 per mile and then 7:56 per mile.
An even split holds one pace from start to finish. A positive split, with a slower second half, is what usually happens when a runner starts too fast, but planning a small one can make sense on a course that gets harder after halfway.
The pace changes exactly at halfway, so the mile or kilometer that contains the halfway point mixes the two paces. Check yourself against the elapsed column at the course markers rather than your GPS watch: courses are measured along the shortest route a runner could take, so watches usually read a little long.