Negative Split Calculator

About this calculator

A negative split means running the second half of a race faster than the first, the pacing pattern most elite marathon and distance performances share because it avoids the glycogen-depletion “wall” that comes from starting too aggressively. Building one means deliberately setting a first-half pace slower than your overall goal average, banking energy to spend on a faster second half rather than hoping to hold on.

Marathon and half-marathon runners plan negative splits ahead of race day because pacing discipline in the first miles is the single biggest predictor of a strong finish — a runner who goes out even a few seconds per mile too fast typically loses far more time in the final miles than they gained early on. Race plans built this way usually target a fixed gap, commonly a range like 1-3% faster in the second half, rather than an even split.

This calculator takes your goal finish time and desired split gap and returns the target time and pace for each half of the race, so you have concrete checkpoints to run against on race day.