Running the second half of a race faster than the first. A 3 hour 30 minute marathon run in 1:46:00 and 1:44:00 is a negative split of about 2%. The opposite, a positive split, is what most recreational marathon fields actually run, because the early miles feel easy at any pace and the cost arrives after 30km.
Small is realistic. A 1% to 2% difference between halves is a common target and is what this calculator defaults to, because it builds a margin without leaving significant time on the table if the second half does not come. A 3% negative split means starting noticeably slower than goal pace, which suits runners who reliably fade or who are racing in heat.
For a flat course in good conditions, an even split is the mathematically efficient way to run a marathon, and most world records are close to even. The argument for a negative split is practical rather than physiological: it protects against the near-universal habit of starting too fast, and it costs very little if you get it right. This calculator shows the even split alongside your chosen one.
Yes. On a course with meaningful elevation change, the halves are not comparable, so pacing by effort beats pacing by the clock. Splitting a downhill first half and an uphill second half evenly on paper means running much harder in the second half. The pace band generator builds elevation-adjusted splits for the Majors instead.
First-half and second-half times and paces, plus a full table of every kilometre or mile split at the two paces, so you can read the plan straight off a watch or a pace band. Switch between kilometres and miles with the toggle at the top of the panel.