Zerdly

Negative Split Planner

Plans first-half and second-half paces for a negative-split race goal time.

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How to use this calculator

Enter details

Distance(km)
Goal time
::
Second half faster by(%)

Result

Fill in the fields to see your result.

Estimate only — real results depend on terrain, weather, fatigue, conditions and individual fitness. Not medical or coaching advice.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the distance, goal time and how much faster you want the second half.
  2. Read each half's time and pace.

How it works

With the second half X% faster: first-half time = goal ÷ (2 − X/100); the rest is the second half.

Worked example

Half marathon, 2% negative. Splits the goal so the back half is ~2% quicker than the front.

Common mistakes

  • Making the negative split too big — a 1–3% faster second half is plenty; more usually means you started too slow.
  • Setting first-half pace by feel on race day, when adrenaline makes easy feel fast.

Tips

  • Times are estimates only — not medical or coaching advice. Always train safely and follow event rules.
  • Distances are editable: choose “Custom…” to enter your own course lengths.

Frequently asked questions

What is a negative split?

Running the second half of a race faster than the first. It conserves energy early and often produces a stronger finish and a faster overall time.

How much faster should the second half be?

Around 1–3% is typical — a few seconds per kilometre — enough to feel controlled early without leaving too much in the tank.

What's a sensible negative split?

1–3% faster is realistic; too aggressive a first half is the more common mistake.

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Cite this tool

Zerdly. (2026). Negative Split Planner. Retrieved from https://www.zerdly.com/tools/negative-split-planner/

Tip: Enter any known values to calculate the remaining results.

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