Negative Split Pace Calculator
Turn a goal finish time into a first-half and second-half pace plan that runs the back half faster — a proven way to race a strong even effort.
How it works
First-half time = Total ÷ (2 − split%) · Second-half time = Total − First-half time · Pace = half-time ÷ (distance ÷ 2)
A negative split means the second half is faster than the first. Starting a touch conservatively spares glycogen and holds effort steady as fatigue climbs, so most personal bests are run this way. This planner splits your goal time so the back half is faster by the percentage you choose, then reports the pace for each half.
Worked example
Half-marathon goal 1:45:00 (6300 s) with a 2% negative split: first-half time = 6300 ÷ 1.98 = 3182 s over 10.55 km ≈ 5:02/km; second half = 3118 s ≈ 4:56/km. The average is 4:59/km.
Frequently asked questions
How big should the negative split be?
For most runners 1–3% is realistic — roughly 3–8 seconds per kilometre. Going out much slower than that forces an unrealistically hard finish; the goal is a small, controlled lift, not a sprint.
Does a negative split really make me faster?
It does not add fitness, but it protects against the classic fade: going out too fast burns carbohydrate early and wrecks the last miles. An even-to-negative split usually yields a faster overall time for the same effort.
Should I use this for a 5K?
You can, but short races are run near threshold throughout, so the split window is tiny (well under 2%). It matters most for the half and full marathon.
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This calculator is for educational purposes. Double-check important results before acting on them.