Split calculator: even and negative splits
A split for every mile or kilometer, the clock time you should see, and where halfway falls.
How the math works
Even splits divide the goal time evenly over the distance. Every full mile (or km) gets the same split, and the last row is the leftover fraction: 0.2188 mi in a marathon, 0.1094 mi in a half, 0.1069 mi in a 5K.
Negative splits run the second half faster than the first. You choose the gap in seconds per mile or km. The calculator puts the first-half pace half a gap above your average and the second-half pace half a gap below it. Because both halves are the same distance, the finish time does not change. The split that contains halfway mixes the two paces.
Clock times are rounded to the nearest second, and each split is the difference between two rounded clock times, so the splits always add up to the goal. That is why an even 9:09/mi marathon shows some 9:09 and some 9:10 splits.
Estimates for planning. Weather, hills, course and fitness on the day all change the result. Formulas and distances reviewed October 21, 2026.