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Negative Split Plan Calculator

Work out negative split plan instantly with clear inputs, formula shown and shareable results.

About Negative Split Plan Calculator

A negative split means running the second half faster than the first, which is how most personal bests and world records are set. Holding back by half the target margin in the first half and pushing by the same amount later keeps the total on target: a 100 minute half marathon with a 2% negative split runs 50:30 then 49:30.

Formulas

First half

first = total x (1 + margin/2) / 2

Second half

second = total - first

Worked example

With the default values below, Negative Split Plan Calculator returns Second Half Faster By of 60. Change any input above and every figure here is recalculated in your browser.

Inputs used

Target total timeminimum 0.1 min
100 min
Race distanceminimum 0.1 km
21.0975 km
How much faster the second half should beaccepts 0–20 %
2 %

Results

Second Half Faster By
60 s
First Half Target
50:30
Second Half Target
49:30
Second Half Pace Per Kilometre
4:42

Step by step

  1. 1Values used
  2. 2First half
  3. 3Second half
  4. 4Second Half Faster By= 60 s
  5. 5First Half Target= 50:30
  6. 6Second Half Target= 49:30
  7. 7Second Half Pace Per Kilometre= 4:42

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • This is an estimate from population-average equations, not a medical or diagnostic assessment. Individual results vary with genetics, training history and technique. Seek advice from a qualified coach or clinician before making significant changes to training.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

This is an estimate from population-average equations, not a medical or diagnostic assessment. Individual results vary with genetics, training history and technique. Seek advice from a qualified coach or clinician before making significant changes to training.

Frequently Asked Questions

Why is a negative split faster overall?

Because starting conservatively spares glycogen and delays the acidosis that forces a slowdown, so you keep more speed available for the end.

How big should the margin be?

One to three percent for most runners. More than five percent usually means the first half was simply too slow.

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Negative Split Plan Calculator | Calcrivo